The Water-Energy Nexus—An Earth Science Perspective

Circular 1407

U.S. Department of the Interior

U.S. Geological Survey
Cover photographs (clockwise): 

A. A drill rig in the Fayetteville Shale gas play of Arkansas. Photograph by Bill Cunningham, 

 U.S. Geological Survey (USGS).

B. Ivanpah Solar Electric Generating System in the Mojave Desert of California. Photograph 

 by NRG Energy, Inc., used with permission.

C. Coalbed methane production water discharge near Tongue River, Montana. Photograph 

 by David A. Nimick, USGS. 

D. Browns Ferry nuclear power station. Photograph by U.S. Nuclear Regulatory Commission. 

E. Farm. Photograph by USGS. 

F. McNenny State Fish Hatchery, South Dakota. Photograph by Michael T. Carter. 

G. Oil pumper. Photograph by Bureau of Land Management. 

H. Cooling towers at nuclear power plant. Photograph by USGS. 

I. Coal-mining operation. Photograph by Bureau of Land Management. 

J. Dam and reservoir. Photograph by USGS.

Background photograph: Yucca Mountain crest. Photograph by U.S. Department of Energy.
The Water-Energy Nexus—An Earth Science Perspective

By Richard W. Healy, William M. Alley, Mark A. Engle, Peter B. McMahon, and Jerad D. Bales

Circular 1407

U.S. Department of the Interior

U.S. Geological Survey
ii

U.S. Department of the Interior

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2015

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as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner.

Suggested citation:

Healy, R.W., Alley, W.M., Engle, M.A., McMahon, P.B., and Bales, J.D., 2015, The water-energy nexus—An earth 

science perspective: U.S. Geological Survey Circular 1407, 107 p., http://dx.doi.org/10.3133/cir1407.

Library of Congress Cataloging-in-Publication Data

Library of Congress Control Number: 2015936977

(http://catalog.loc.gov/)

ISSN 1067-084X (print)

ISSN 2330-5703 (online)

ISBN 978-1-4113-3880-7
iii

Contents

Executive Summary.......................................................................................................................................1

Introduction.....................................................................................................................................................3

Water in Energy Production and Use .........................................................................................................6

Fuel Extraction and Processing..........................................................................................................6

Natural Gas and Oil .....................................................................................................................6

Water Use ............................................................................................................................9

Natural Gas.................................................................................................................9

Oil .......................................................................................................................15

Water Quality.....................................................................................................................17

Infrastructure and Development Practices.........................................................17

Produced Water.......................................................................................................22

Coal .........................................................................................................................................23

Water Use ..........................................................................................................................25

Water Quality.....................................................................................................................28

Uranium .......................................................................................................................................28

Water Use ..........................................................................................................................29

Water Quality.....................................................................................................................30

Biomass.......................................................................................................................................30

Water Use for Bioethanol................................................................................................31

Water Use for Biodiesel...................................................................................................32

Water Quality and Biofuels .............................................................................................33

Electrical Power Generation.............................................................................................................33

Thermoelectric Power Plants..................................................................................................33

Water Use for Thermoelectric Plants............................................................................33

Power Plant Thermal Efficiency............................................................................34

Power Plant Cooling Systems................................................................................35

Water Withdrawal ...................................................................................................36

Water Consumption—Carbon-Fuel and Nuclear Plants...................................37

Water Consumption—Geothermal Plants ...........................................................40

Water Consumption—Concentrating Solar Power Plants ...............................41

Water Quality and Thermoelectric Power Plants........................................................42

Coal .......................................................................................................................42

Natural Gas...............................................................................................................43

Nuclear......................................................................................................................43

Biomass.....................................................................................................................47

Hydroelectric Power Plants.....................................................................................................48

Wind and Passive Solar............................................................................................................49

Summary Water Requirements—Electricity and End-Use Sectors...........................................49

Electricity.....................................................................................................................................50

Transportation ............................................................................................................................52

Industrial......................................................................................................................................53

..........

.......

.......
iv

Residential and Commercial ....................................................................................................53

Comparison of Water Consumption for Electricity and End-Use Sectors........................53

Energy for Water Development, Distribution, and Use..........................................................................56

Water Conveyance .............................................................................................................................57

Groundwater...............................................................................................................................57

Surface Water............................................................................................................................58

Water Treatment .................................................................................................................................60

Water Distribution...............................................................................................................................62

End Use.................................................................................................................................................62

Wastewater Collection ......................................................................................................................65

Wastewater Treatment ......................................................................................................................65

Summary of Water-Related Energy Use .........................................................................................68

Science for Addressing the Water-Energy Nexus.................................................................................69

Monitoring and Assessment.............................................................................................................69

Monitoring Networks ................................................................................................................69

Available Freshwater ................................................................................................................71

Water Quantity Monitoring..............................................................................................73

Water Quality Monitoring ................................................................................................73

Water Use ...................................................................................................................................75

Ecosystems.................................................................................................................................76

Saline Groundwater Availability..............................................................................................78

Fossil Fuels and Uranium..........................................................................................................79

Geothermal Resources .............................................................................................................79

Induced Seismicity ....................................................................................................................80

Data Analysis Tools ...................................................................................................................81

Research ..............................................................................................................................................83

Climate Change ..........................................................................................................................83

Byproducts and Waste Streams of Energy Development...................................................85

Emerging Energy Development Technologies ......................................................................87

Energy Use for Water................................................................................................................88

Conclusions...................................................................................................................................................90

References Cited..........................................................................................................................................91

Photograph Credits....................................................................................................................................106
v

Figures

1. Diagram showing the major steps in energy development that consume water..............6

2. Illustration showing categories of conventional and unconventional hydrocarbon

occurrences ..................................................................................................................................7

3. Graphs showing annual domestic production of natural gas and oil (including

natural gas plant liquids) in the United States, 1950–2013.....................................................7

4. Map showing shale plays of the conterminous United States .............................................8

5. Map showing oil and water production and water and CO2 injection as part of

primary, secondary, and tertiary production periods for the Denver Unit of the

Wasson Field, west Texas, 1938–1988, with enhanced oil recovery during tertiary

production indicated ..................................................................................................................15

6. Schematic of a modern vertical oil or gas well.....................................................................19

7. Graphs showing the relative production of water and hydrocarbons from a

conventional oil well, a shallow conventional gas well, a coalbed natural gas well,

and a shale gas well...................................................................................................................22

8. Map showing coal fields of the United States classified by rank ......................................24

9. Idealized cross section illustrating in-place recovery of uranium using chemical

leaching compounds..................................................................................................................29

10. Graph showing annual production of biofuels in the United States, 1981–2013..............30

11. Graph showing annual hectares of planted corn in the United States, 2000–2013.........31

12. Pie diagram showing total electricity generation in the United States by fuel, 2013......33

13. Graph showing monthly net electricity generation in the United States by source,

January 2011–December 2012..................................................................................................35

14. Schematic and general characteristics of a stream thermoelectric power plant

with water cooling, once-through cooling system, and wet recirculating systems

with cooling towers....................................................................................................................36

15. Maps showing freshwater and saline-water withdrawals for thermoelectric power

generation by State, 2010 ..........................................................................................................37

16. Graph showing annual electricity generation in the United States by fuel, 

1950–2013 .....................................................................................................................................37

17. Map showing locations of the 100 operational commercial nuclear power reactors

in the United States as of 2014 .................................................................................................39

18. Map showing relative favorability of occurrence of geothermal resources in the

western contiguous United States. .........................................................................................40

19. Pie diagram showing primary energy consumption in the United States for

electricity generation and four end-use sectors, 2013, as a percentage of the total

consumption of 28.5 trillion kilowatthours of thermal energy .............................................49

20. Pie diagram showing total energy consumption for the United States by end-use

sector, 2013, as a percentage of the total consumption of 28.5 trillion kilowatthours

of thermal energy........................................................................................................................49

21. Graph showing estimated range of water consumption for the generation of

electricity in the United States by method of generation, 2013 ..........................................51

22. Graph showing estimated water consumption for the production of transportation

fuels in the United States, 2013 ................................................................................................53

23. Graph showing estimated energy-related water consumption in the residential

end-use sector of the United States by fuel, 2013.................................................................54
vi

24. Graph showing estimated energy-related water consumption in the commercial

end-use sector of the United States by fuel, 2013.................................................................55

25. Graph showing estimates of total energy-related water consumption in the United

States by end-use sector, 2013.................................................................................................55

26. Pie diagam showing total water withdrawals in the United States by 

category, 2010..............................................................................................................................56

27. Diagram showing a generalized water-use cycle ................................................................56

28. Schematic representation of the process used by the Denver Water public agency

to treat surface water................................................................................................................60

29. Graph showing typical energy intensities associated with the conveyance and

treatment of water, by source ..................................................................................................61

30. Schematic showing summertime treatment processes at Clean Water Services’

wastewater treatment facility in Durham, Oregon................................................................65

31. Graph showing annual water-related energy use in the residential and commercial

sectors of the United States, 2005 ...........................................................................................68

32. Map showing surface-water availability as defined by a metric based on measured

streamflow and current water use ..........................................................................................72

33. Map showing water-level changes in the High Plains aquifer, from predevelopment

to 2011...........................................................................................................................................74

34. Map showing the Wyoming Landscape Initiative area, including 

surface jurisdiction.....................................................................................................................77

35. Generalized map of the depth to saline groundwater for the conterminous United

States............................................................................................................................................78

36. Graph showing cumulative count of earthquakes with magnitude greater than 3 in

the central and eastern United States, 1967–2012................................................................81

37. Schematic showing a framework for the integration of groundwater monitoring and

groundwater flow modeling......................................................................................................82

38. Graph showing annual global mean surface temperature anomalies from three

data sets, and annual global mean sea level anomalies reconstructed from tide

gages by three different approaches......................................................................................83

39. Maps showing predicted temperature change, in degrees Celsius, for western

North America for June–August for the period 2081–2100 relative to average

temperature for 1986–2005........................................................................................................84

40. False color map showing the response from helicopter electromagnetic surveys 

for a portion of the Salt Creek oilfield near Casper, Wyoming............................................87
vii

Tables

1. Water consumption for different steps in production of natural gas, oil, coal, and

uranium...........................................................................................................................................9

2. Energy contents of selected fuels ...........................................................................................34

3. Power plant thermal efficiency and water consumption rates for different types of

electricity generation in terms of water intensity .................................................................34

4. Estimates of water consumption in the United States for different types of

electricity generation in terms of water intensity (in liters of water per kilowatthour

of generated electricity) and in terms of total water consumed in 2013...........................51

5. Estimates of water consumption in the United States for different types of

transportation fuels in terms of rates of consumption and in terms of total water

consumed in 2013 .......................................................................................................................52

6. Estimates of energy and related water consumption for primary and total energy

consumption for the residential end-use sector in the United States in 2013..................54

7. Estimates of energy and related water consumption for primary and total energy

consumption for the commercial end-use sector in the United States in 2013 ...............54

8. Estimates of energy and energy-related water consumption in the United States in

2013, by end-use sector.............................................................................................................55

9. Percentage of community water-treatment plants using different treatment 

schemes .......................................................................................................................................60

10. Estimated energy savings for selected water technologies...............................................61

11. Estimated energy intensity of heating water for selected residential water uses..........64

12. Energy value of water saved as the result of the implementation of selected

water-efficiency measures in California, 2004.......................................................................64
viii

Box Topics

A Energy Consumption in the United States ..........................................................................................4

B Water Availability and Usage in the United States .........................................................................10

C Hydraulic Fracturing.............................................................................................................................12

D The Marcellus Shale—A Vast Energy Resource with Important Challenges ............................16

E A Tale of Two Basins—Water Surplus/Water Deficit.....................................................................18

F Gasoline Additives—Clean Air vs Clean Water? The MTBE Story...............................................20

G Produced Waters—An Underused Resource?................................................................................23

H Subsurface Fluid Injection—Risks of Groundwater Contamination and Earthquakes .............26

I Droughts and Energy Development ...................................................................................................38

J Energy, Atmospheric Emissions, and Water Quality.......................................................................44

K Carbon Capture and Sequestration ...................................................................................................46

L Managed Aquifer Recharge of Recoverable Water .......................................................................59

M The Energy Intensity of Bottled Water ..............................................................................................63

N Recycled Water in California ..............................................................................................................66

O Piceance Basin Water-Quality Data Repository—A Tool for Water-Resource 

Monitoring Related to Energy Development..........................................................................70

P Saving Energy and Saving Water.......................................................................................................89

Figures

A–1. Graph showing total annual energy consumption, production, imports, and exports

for the United States, 1950–2013 ................................................................................................4

A–2. Graph showing estimated energy consumption for the United States by energy

source and energy-use sector, 2013, in trillions of kilowatthours of thermal energy .......5

B–1. Schematic of a watershed showing components of a water-budget equation...............10

B–2. Map showing average annual precipitation in the conterminous United States,

1981–2010, as determined with the PRISM dataset..............................................................11

B–3. Graph showing trends in water withdrawal by water-use category, 1950–2010.............11

C–1. Illustration showing cross-section view of a hydraulically fractured shale 

gas well ........................................................................................................................................12

C–2. Graph showing annual estimates of natural gas reserves in the United States,

1980–2012 .....................................................................................................................................12

C–3. Pie diagrams showing relative volume of the various materials used to

hydraulically fracture an oil well in the Texas portion of the Permian Basin, from 

a total volume of 4.5 million liters.............................................................................................13

C–4. Graph showing approximate depth of zones of shallow, fresh groundwater sources

relative to reservoir depths for important shale gas reservoirs of the United States.....14
ix

D–1. Map showing the extent of the Appalachian Basin Province and the three

assessment units of the Marcellus Shale used in its resource assessment ...................16

E–1. Map showing Powder River Basin and Williston Basin.......................................................18

E–2. Graph showing water production for coalbed natural gas in the Powder River

Basin, Wyoming, 2002–2013......................................................................................................19

E–3. Graph showing annual oil production in North Dakota, primarily from the Williston

Basin, 1950–2013.........................................................................................................................19

F–1. Map showing locations where methyl tertiary butyl ether was detected in

groundwater in the United States, 1985–2001........................................................................21

H–1. Schematics showing Class I, II, and III wells, as defined by the U.S. Environmental

Protection Agency Underground Injection Control Program..............................................27

I–1. An example of a drought index map developed on the basis of percentile of 7-day

average streamflow relative to historical streamflow on a given day of the year..........38

J–1. Pie diagram showing relative contributions to the total greenhouse gas emissions

for the United States, 2011, as a percentage of the total emissions of 6.7 billion

metric tons of carbon dioxide equivalent...............................................................................44

J–2. Graph showing mean annual atmospheric carbon dioxide concentrations as

measured at Mauna Loa, Hawaii, 1959–2013.........................................................................45

J–3. Maps showing average annual pH values in precipitation for 1985 and 2012

indicate a substantial reduction in acid deposition over this period.................................45

J–4. Illustration showing environmental pathways for mercury emitted to the

atmosphere and potential for uptake and bioaccumulation in aquatic organisms.........45

K–1. Illustration showing the concept of geologic carbon sequestration.................................46

N–1. Pie diagram showing the State of California’s use of recycled wastewater, 2001, as

a percentage of the total amount of about 0.6 trillion liters.................................................66

N–2. Schematic illustration of some possible direct and indirect uses of recycled

wastewater..................................................................................................................................66

N–3. Graph showing relative energy intensity of selected water sources in southern

California ......................................................................................................................................67

O–1. Map showing location of producing oil and gas wells, oil shale deposits, and major

rivers in the Piceance Basin, Colorado...................................................................................70

Tables

H–1. Class, use, and number of wells in the U.S. Environmental Protection Agency

Underground Injection Control Program in the United States in 2011...............................26

H–2. Summary information on reported “felt” seismic events that could be attributed to

energy-related activities ...........................................................................................................27

J–1. Gaseous and particulate emissions from the uncontrolled combustion of common

fossil fuels. Hard coal refers to bituminous and subbituminous coal................................44

M–1. Energy requirements for producing bottled water................................................................63
x

Conversion Factors

SI to Inch/Pound

Multiply By To obtain

Length

millimeter (mm) 0.03937 inch (in.)

meter (m) 3.281 foot (ft) 

kilometer (km) 0.6214 mile (mi)

Area

hectare (ha) 2.471 acre

square kilometer (km2

) 247.1 acre

square meter (m2

) 10.76 square foot (ft2) 

hectare (ha) 0.003861 square mile (mi2

) 

square kilometer (km2

) 0.3861 square mile (mi2)

Volume

cubic meter (m3

) 6.290 barrel (oil, 1 barrel = 42 gal)

liter (L) 0.2642 gallon (gal)

cubic meter (m3

) 264.2 gallon (gal) 

cubic meter (m3

) 0.0002642 million gallons (Mgal) 

cubic meter (m3

) 35.31 cubic foot (ft3)

cubic meter (m3

) 0.0008107 acre-foot (acre-ft) 

cubic hectare (ha3

) 810.7 acre-foot (acre-ft) 

Flow rate

cubic meter per year (m3

/yr) 0.000811 acre-foot per year (acre-ft/yr) 

meter per second (m/s) 3.281 foot per second (ft/s) 

cubic meter per second (m3

/s) 35.31 cubic foot per second (ft3/s)

cubic meter per day (m3

/d) 264.2 gallon per day (gal/d) 

millimeter per year (mm/yr) 0.03937 inch per year (in/yr) 

Mass

kilogram (kg) 2.205 pound avoirdupois (lb)

metric ton per day 1.102 ton per day (ton/d) 

Energy

joule (J) 0.0000002 kilowatthour (kWh)

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F=(1.8×°C)+32
The Water-Energy Nexus—An Earth Science Perspective

By Richard W. Healy, William M. Alley, Mark A. Engle, Peter B. McMahon, and Jerad D. Bales

Executive Summary

Water availability and use are closely connected with energy development and use. Water 

cannot be delivered to homes, businesses, and industries without energy, and most forms of 

energy development require large amounts of water. The United States faces two significant and 

sometimes competing challenges: to provide sustainable supplies of freshwater for humans and 

ecosystems and to ensure adequate sources of energy for future generations. This report reviews 

the complex ways in which water and energy are interconnected and describes the earth science 

data collection and research that can help the Nation address these important challenges.

A full understanding of the water-energy nexus is limited by uncertainty in our knowledge 

of fundamental issues, such as the quantity of freshwater that is available, the amount of water 

that is used in energy development, the effects that emerging energy development technologies have on water quality and quantity, and the amount of energy required to treat and deliver 

freshwater. Nevertheless, some findings are clear: reducing the use of freshwater and protecting it from contamination conserve energy, and reducing energy use conserves water. Water 

withdrawn for energy-related operations represents about 45 percent of all withdrawals in 

the United States; water consumption for these operations represents about 2–5 percent of all 

withdrawals. Withdrawn water that is not consumed is returned to its original source or another 

water body. Water resources and energy operations are not evenly distributed across the United 

States. In arid and semiarid western regions, freshwater resources are limited. Increased rates of 

extraction of oil and natural gas in some of these regions raise concerns about water availability 

for traditional agricultural, municipal, and domestic water users and for ecosystems. Populations are predicted to grow in these western areas in coming decades, so demands for water and 

energy will likely increase, and competition for limited supplies of freshwater might intensify.

Electricity generation accounts for most energy-related water withdrawal. Hydroelectric, 

geothermal, and concentrating solar power plants use renewable sources to generate electricity 

with low carbon emissions; however, these plants generally consume more water per kilowatthour of generated electricity than power plants that use nonrenewable sources, such as coal, 

natural gas, and nuclear power. Production of biofuels is more water intensive than 

production of hydrocarbon fuels—biofuels make up about 5 percent of transportation 

fuels in the United States, yet irrigation of crops used to make those fuels consumes 

as much as one half of the total amount of water consumed in production of all 

transportation fuels. Energy use for development of water resources is difficult to 

quantify, but heating water for washing and cooking is estimated to account for 

more than 70 percent of the total amount of energy used to withdraw, treat, 

and convey water to and from homes and commercial establishments.

Mallik gas hydrate production test research project.
2 The Water-Energy Nexus—An Earth Science Perspective

Decisions on development of water and energy resources are complicated by a number of tradeoffs, including 

• the reduced greenhouse gas emissions from some renewable energy 

sources versus the added amount of water required to develop 

these sources, 

• the improved air and water quality from implementation of carbon 

capture and geologic sequestration versus the additional fuel and 

water required for that implementation, 

• the reduced amount of water needed for dry-cooled thermoelectric 

power plants versus the higher fuel requirements for these systems 

during hot summer months, and 

• the large increase in recoverable oil and natural gas reserves 

brought on by technologies such as directional drilling and hydraulic fracturing versus the unknown environmental costs of the 

technologies. 

The benefits and costs of tradeoffs such as these need to be weighed, 

but coordinated planning among energy developers, water developers, 

water-resource managers, and ecosystems managers can result in mutual 

benefits.

The earth sciences have been a cornerstone in developing our current understanding of the water-energy nexus. Continued data collection 

and research can reduce the uncertainty that limits our knowledge of 

many important water-energy issues and thereby lay the groundwork for 

informed resource management. Relevant earth science issues analyzed 

and discussed herein include freshwater availability; water use; ecosystems health; assessment of saline water resources; assessment of fossilfuel, uranium, and geothermal resources; subsurface injection of wastewater and carbon dioxide and induced seismicity; climate change and its 

effect on water availability and energy production; byproducts and waste 

streams of energy development; emerging energy-development technologies; and energy for water treatment and delivery.

The intent of this report is to provide scientific insight to resource 

managers and the general public on the complex ways in which water and 

energy are interconnected and to highlight the important issues that affect 

availability and sustainability of water and energy resources in the United 

States. The goals of preserving sustainable supplies of freshwater for 

humans and ecosystems and ensuring sufficient energy resources for future 

generations are not mutually exclusive, but prudent resource management 

is required to attain them; the earth sciences provide the basis for informed 

resource-management decisions.

Livestock well with solar-powered pump.
Introduction 3

Introduction

Water and energy are essential to human existence. 

Humans need water to drink, to grow crops, to extract fuels 

and minerals, to generate power, and to manufacture goods; 

we embrace water for its aesthetic values and recreational 

opportunities; and the health of ecosystems depends on the 

availability of water. Likewise, energy harnessed for human 

use from conversion of resources such as coal, oil, natural gas, 

uranium, water, wind, and the sun provides more than mere 

conveniences. The produced energy sustains a large, vibrant 

civilization that supports living environments, food production, industry, science, commerce, transportation, entertainment, and much more. Americans have become heavily reliant 

on the availability of affordable power. 

Water and energy resources are intrinsically linked in 

many important ways. Energy is required to withdraw water, 

to treat water for human consumption, and to transport water. 

At the same time, water is required to extract and process fossil fuels, to grow biofuels, and to cool thermoelectric power 

plants. The availability and economic feasibility of developing either water or energy resources depends largely on the 

availability and cost of the other resource. Limits on available 

water may preclude development of some energy resources, 

just as a lack of electrical power may hinder capabilities to 

extract, treat, and transport water. A detailed examination of 

the links between water and energy can enhance capabilities 

of resource managers to provide freshwater for people and 

ecosystems and to ensure sufficient power to support human 

lifestyles. Such an examination can also generate greater public awareness of issues that affect the availability of water and 

energy resources.

The United States is relatively rich in water and energy 

resources, but they are not evenly distributed across the country. In regions where available supplies of water are limited, 

there is a long history of competition for that water among 

traditional agricultural, municipal, industrial, and energy 

interests (Reisner, 1993). This competition might increase as 

populations grow, extraction of oil and natural gas increases, 

and the effects of energy development on water quantity and 

quality become more apparent. Prospects for avoiding future 

water and energy conflicts may be improved if there is an 

appreciation on the part of all interested parties of the limited 

availability of water and fossil fuels and the interdependence 

of water development and energy development.

This report provides an overview of the important ways 

in which water and energy are interconnected. The report is 

aimed primarily toward water- and energy-resource managers 

in the United States; however, the material is presented in a 

way that will appeal to large segments of the general public. 

The objective of this report is to provide readers with scientific 

insight to the challenges to be overcome as Americans strive 

to develop a sustainable supply of freshwater for humans and 

ecosystems while at the same time ensuring the availability 

of energy resources for future generations. These are complex 

challenges, and to address them in a comprehensive manner requires the consideration of economic, human-health, 

cultural, and societal issues. But key to any analysis of the 

water-energy nexus is a firm understanding of fundamental 

earth science issues, including the availability of water and 

energy resources; the extraction, processing, and conservation 

of these resources; and the protection of water resources for 

humans and ecosystems. 

The section “Water in Energy Production and Use” 

describes and explains the water needs for energy production and use along with associated water-quality issues. The 

amount of water required to deliver a kilowatthour (kWh) 

of electricity to a home is calculated for all steps from fuel 

extraction and processing, through generation and delivery of 

electricity, to final disposal of byproducts. The section “Energy 

for Water Development, Distribution, and Use” presents an 

analysis of the energy requirements for withdrawing, treating, 

and delivering water; energy use is given in terms of kilowatthours per liter of water. The analyses in these two sections 

facilitate comparison of the costs (in terms of water) for different types of energy production, as well as the cost (in terms 

of energy) for withdrawing, treating, and delivering water. 

The section “Science for Addressing the Water-Energy Nexus” 

contains a discussion of the role that the earth sciences play in 

addressing the important interrelated energy and water issues.

Dam and reservoir.

Continued on page 6
4 The Water-Energy Nexus—An Earth Science Perspective

Working with numbers for energy production can be confusing because the volume, mass, 

and energy content of individual fuels are often 

reported in unique sets of units. Oil volume is 

reported in barrels, natural gas volume is reported in million cubic feet, and coal mass is reported in tons or metric 

tons. The International System of Units (SI) is used in this 

report, and energy is reported in kilowatthours—a unit 

equivalent to one kilowatt of energy use for a period of 

one hour. Both electrical energy and thermal energy—the 

energy content of a fuel—are expressed in kilowatthours. In 

this report, kilowatthours of electricity use the abbreviation 

kWh, and kilowatthours of thermal energy use the abbreviation kWhth. Factors for converting energy, volumes, 

masses, and energy contents to more familiar units are 

provided in the table on page x.

Annual energy consumption in the United States 

has followed a general upward trend since 1949, reaching a level estimated to be 28.5 trillion kWhth, or about 

90,000 kWhth per person, in 2013 (fig. A–1; U.S. Energy 

Information Administration, 2014b). The 90,000 kWth are 

equivalent to the amount of energy contained in 11 metric 

tons of coal or about 10,000 L of gasoline.

Energy Consumption in the United States

Most of the energy we consume is produced from fossil 

fuels—oil, natural gas, and coal (fig. A–2). Oil is used primarily for transportation purposes (for example, gas and diesel 

fuel for cars and buses, and jet fuel for aircraft). Natural gas is 

used for industrial purposes, for heating residential and commercial buildings, and for generating electric power. Coal is 

the most widely used fuel for generating electricity, although 

natural gas, nuclear energy, and renewable energy are also 

used for this purpose. Renewable energy is used in a wide 

spectrum of sectors.

For electric power, the numbers in figure A–2 represent 

the energy consumed by power plants (11.2 trillion kWhth); 

however, the energy consumed is not equal to the energy 

(in the form of electricity) that is delivered to an end point. 

As will be described in subsequent sections, energy losses 

occur in the production and transmission of electricity. Of the 

11.2 trillion kWhth consumed by power plants, only 3.9 trillion 

kWh of electrical energy were actually delivered to customers; 

approximately 65 percent of the consumed energy was lost as 

heat or other forms of energy that are not captured for human 

use. 

A 20-watt light bulb turned 

on for 1 hour uses 20 watt 

hours or 0.02 kilowatthours 

of electricity.

Consumption

Production

Imports

Exports

EXPLANATION

0

5

10

15

20

25

30

35

1950 1960 1970 1980 1990 2000 2010 2020

Thermal energy, in trillions of kilowatthours 

Year

Figure A–1. Total annual energy consumption, production, imports, and exports for the 

United States, 1950–2013. (U.S. Energy Information Administration, 2014b)
Residential and

commercial

3.1 (11 percent)

Industrial

6.3

(22 percent)

Electric power

11.2

(39 percent)

Natural gas

7.8

(27 percent)

Coal

5.3

(19 percent)

Nuclear 

electric power

2.4 (8 percent)

Renewable

energy

2.7 (10 percent)

Oil

10.2

(36 percent)

Percent

of

sources

Total equals 

28.5 trillion

kilowatthours

of thermal 

energy

Percent

of

sectors

71

25

4

1

3

34

32

31

9

<1

91

22

100

13

24

11

13

52

40

12

10

1

9

7

42

79

92

5

3

<1

22

43

Transportation

7.9

(28 percent)

Introduction 5

Figure A–2. Estimated energy consumption for the United 

States by energy source and energy-use sector, 2013, in 

trillions of kilowatthours of thermal energy. Oil includes natural 

gas liquids. (U.S. Energy Information Administration, 2014b)

Domestically produced fuels accounted for approximately 75 percent of energy consumption in the United States 

in 2013; imported fuels accounted for the remaining 25 percent. The reliance of the United States on imported fuels has 

been in decline since 2006 when imported fuels accounted for 

35 percent of total consumption. Imported fuel is primarily 

oil—net imports accounted for approximately 33 percent of 

all oil consumed in the United States in 2013, whereas in 2006 

they accounted for over 60 percent (U.S. Energy Information 

Administration, 2014b).

Coal mining operation.

A water impoundment at a drill pad in the 

Fayetteville Shale gas play of Arkansas.

Fossil fuel extraction.
Fossil fuel extraction

Noncombustibles

Biomass growth

Electricity generation

Processing

Commercial

IndustrialIndustrial

Transportation

ResidentialResidential

Fuels

End use

6 The Water-Energy Nexus—An Earth Science Perspective

Water in Energy Production and Use

Water is associated with all steps of energy development, including fuel extraction and processing, generation of 

electricity, and final end use (fig. 1). The water needs for each 

of these steps are described within this section; in addition, 

estimates of total water consumption are summarized for 

electricity generation and for each of the energy-use sectors 

as defined by the U.S. Energy Information Administration 

(2014a): residential, commercial, industrial, and transportation. Water requirements for fuel extraction and processing are 

provided in terms of the amount of water required for extracting and processing a unit volume or mass of fuel (for example, 

liters of water per cubic meter of natural gas or liters of water 

per liter of gasoline). For electricity generation and end use, 

water-consumption numbers are converted to water intensities: volume of water consumed (in liters) per unit of generated electricity (in kilowatthours). The use of water intensities 

facilitates the comparison of water consumption rates for 

different fuels and different energy uses. 

The distinction between water withdrawal and water 

consumption must be clear in the reader’s mind. As described 

in Box B, water withdrawal is the extraction of water from 

surface-water or groundwater sources, water use refers to 

water withdrawal for a specific purpose, and water consumption is that part of withdrawn water that is evaporated or 

removed from the immediate water environment by some 

other means. These terms are not used consistently in all 

reports, which can cause confusion and uncertainty. Some 

reports make no distinction between withdrawal and consumption rates, and some reports provide only consumption rates. 

For many energy development operations, withdrawal 

and consumption rates are 

similar, but for operations at 

thermoelectric power plants, 

water consumption rates can 

be just a small fraction of 

withdrawal rates.

Water-quality problems can arise in all areas 

of energy development and 

use. Water contamination 

can result from a variety of 

factors, including improper 

procedures, faulty infrastructure, weak regulations, and 

acts of nature. It can occur 

through direct pathways, 

such as leaks in pipes or 

storage tanks and injection of fluids into wells, or 

through indirect pathways, 

such as acid-mine drainage 

Figure 1. Major steps in energy development that consume water.

from abandoned mine spoils and atmospheric emissions from 

power plants and motor vehicles. 

Fuel Extraction and Processing

The energy that Americans consume comes from a 

number of different fuels and natural resources. Electricity 

is generated from coal, natural gas, and uranium and from 

flowing water, geothermal heat, wind, and the sun. Homes and 

businesses are heated by natural gas, electricity, wood, fuel oil, 

and coal. Motor vehicles are powered by hydrocarbon fuels 

and biofuels and increasingly by electricity. Water is involved 

in virtually every step of extracting, growing, and processing these fuels. Water use and associated water-quality issues 

associated with fuel sources—natural gas, oil, coal, uranium, 

and biomass—are described in the following sections. (See 

the section “Electrical Power Generation” for discussions on 

thermoelectric, hydroelectric, wind and solar sources.) 

Natural Gas and Oil

Natural gas and oil together account for more than 

60 percent of all energy consumption in the United States on 

an annual basis. We group oil and natural gas together in this 

section because they are related geologically and because 

techniques for extracting the two are similar. In 2013, the 

United States consumed about 0.95 trillion liters (L) of oil 

(U.S. Energy Information Administration, 2014b), equivalent 
Water in Energy Production and Use 7

to 10.2 trillion kilowatthours 

of thermal energy.1 Most oil 

is used for transportation 

fuels—gasoline, diesel fuel, 

and jet fuel—with smaller 

amounts used for industry, 

home heating, and generation of electricity. Natural 

gas consumption in 2013 

was about 740 billion m3

, 

or about 7.8 trillion kWhth

of energy (U.S. Energy 

Information Administration, 2014b). Natural gas is 

used for heating residential 

and commercial buildings, 

heating water, industrial 

purposes, and generation of 

electricity.

Natural gas and 

oil resources typically 

are categorized into two 

broad groups: conventional and unconventional resources 

(Schenk and Pollastra, 2002). Conventional resources refer 

to oil and natural gas that have migrated from a source rock 

into a discrete geological trap where a well-defined waterhydrocarbon contact exists (fig. 2). By comparison, unconventional hydrocarbon resources, also referred to as continuous 

resources, consist of oil and natural gas dispersed through one 

or more geologic layers with no obvious water-hydrocarbon 

contact. Examples of unconventional resources include shale 

gas; coalbed natural gas; gas in low-permeability sandstones, 

siltstones, and carbonates (referred to as tight gas); oil in lowpermeability sandstones and shales (referred to as tight oil); oil 

shale; and oil sands. 

Domestic production of both natural gas and oil has 

increased steadily since 2005 (fig. 3), and that trend is 

expected to continue (U.S. Energy Information Administration, 2012b). The increased productivity is from unconventional sources and is the direct result of better geologic 

understanding of these resources and advanced techniques 

employed by the energy industry. The two most important 

of these techniques are directional well drilling and hydraulic fracturing (fracking). Directional drilling allows wells to 

extend several kilometers horizontally within an oil or gas 

reservoir and to intercept multiple discrete production zones. 

In addition, several wells can be drilled in different directions 

from a single well pad, thus minimizing infrastructure requirements and surface footprints. Hydraulic fracturing is a method 

1

Thermal energy refers to the energy content of the fuel, as opposed to electrical energy generated from consuming that fuel, which is also expressed in 

terms of kilowatthours; for clarity in notation throughout the remainder of the 

report the term kWhth is used to represent kilowatthours of thermal energy, and 

the term kWh is used to represent kilowatthours of electrical energy.

Figure 2. Categories of conventional and unconventional hydrocarbon occurrences. (From Schenk 

and Pollastro, 2002)

EXPLANATION

Gas

Oil

Water

Unconventional-gas

accumulation

Tens of kilometers

Figure 3. Annual domestic production of (A) natural gas and 

(B) oil (including natural gas plant liquids) in the United States, 

1950–2013. (U.S. Energy Information Administration, 2014b)

0

100

200

300

400

500

600

700

800

Natural gas production, in billion cubic meters 

0

100

200

300

400

500

600

700

1950 1960 1970 1980 1990 2000 2010 2020

Oil production, in billions of liters

Year

A

B
8 The Water-Energy Nexus—An Earth Science Perspective

Shale plays

Prospective play

Current play

Basin and name

EXPLANATION

Shallowest/youngest

Intermediate depth/age

Deepest/oldest

Stacked plays

Source: Energy Information Administration, based on data from 

various published studies, updated May 9, 2011

TX-LA-MS

Salt Basin

Floyd-Neal

Valley and Ridge

Province

Pearsall

Conasauga

Avalon-Bone Spring

Barnett-Woodford

Western

Gulf

Marfa

 Basin

Ft. Worth

Basin

Permian

Basin

Tuscaloosa

Eagle

Ford

0 200 400 600

800 KILOMETERS

800 MILES

0 200 400 600

HaynesvilleBossier

Fayetteville

Woodford

Barnett

Bend

Palo Duro

Basin

Black Warrior

Basin Chattanooga

Arkoma Basin

Devonian (Ohio)

Marcellus

Utica

Appalachian

Michigan Antrim Basin

Basin

Forest City

Basin

New

Albany

Illinois

Basin

Excello-Mulky Cherokee Platform

Denver

Basin

Anadarko

Basin

Niobrara

Mowry

Powder

River

Basin

Big

Horn

Basin

Gammon

Bakken

Williston

Basin

Heath

Niobrara

Cody

Montana

Thrust

Belt

Hilliard-Baxter-Mancos

Greater

Green

River

Basin

Park

Basin

Piceance

Basin

Uinta Basin

Manning Canyon

Mancos

Hermosa

Paradox Basin

Lewis

San Juan

Basin

Pierre

Raton

Basin

MontereyTremblor

San

Joaquin

Basin

Monterey

Santa Maria,

Ventura,

Los Angeles

Basins

TX-LA-MS

Salt Basin

Pearsall Shale play name

Figure 4. Shale plays of the conterminous United States. (U.S. Energy Information Administration, 2011)

for enhancing the permeability of the reservoir rock by applying high pressure to isolated sections of the well bore to create 

fractures in the rock (see Box C—Hydraulic Fracturing). 

Together, these techniques have made it possible to capture oil 

and natural gas contained in shale and sandstone formations 

that cover vast swaths of the United States (fig. 4). In the past, 

those resources were considered largely inaccessible. 

Water is involved in all stages of natural gas and oil 

development, including exploration, production, and processing. Some stages require minimum amounts of water; others 

require substantial quantities—hydraulic fracturing of a single 

well may require millions of liters of water. In addition, water 

often is extracted along with oil and natural gas; this water 

is referred to as produced water, and it can consist of native 

water present in the geologic formation prior to development 

and fluids and chemicals injected into the formation to stimulate production. Water requirements and the quantity and quality of produced water in oil and natural gas development are 

affected by a number of factors, including the type of energy 

resource being developed, the local and regional geology and 

hydrology, and the processes that are used in development. As 

will be discussed in subsequent sections, a shortage of quantitative data and the large variability in natural conditions across 

the United States lead to a substantial uncertainty in estimates 

of water requirements for development of oil and natural gas. 

Water-quantity and quality issues associated with exploration, 

production, and processing of natural gas and oil are addressed 

in the following sections.
Water in Energy Production and Use 9

Water Use

Natural Gas

Water is a key ingredient in drilling fluids. These fluids 

serve multiple purposes in well drilling, including floating 

crushed rock and sediment from the drill bit to land surface, 

lowering friction between the drill bit and rock, and cooling 

moving parts in drilling systems. Estimates of the volume of 

water required for drilling a well vary widely and depend on 

the well length, diameter, and amount of water loss to the surrounding formations. Conventional onshore vertical gas wells 

generally require negligible amounts of water for drilling and 

gas extraction (International Energy Agency, 2012b). Horizontal shale gas wells that extend several kilometers typically 

require more water than vertical wells for drilling, but the 

amount of water used for drilling is still small relative to that 

for well stimulation (Nicot and Scanlon, 2012).

Extraction of shale gas and tight gas usually requires 

some kind of fracture stimulation. Several techniques for 

inducing fractures can be used, but water-intensive hydraulic fracturing is probably the most common technique (see 

Box C—Hydraulic Fracturing). Water requirements for 

hydraulic fracturing vary depending on geology and well 

design. One operator reports a range of 0.1 to 0.2 liters of 

water per cubic meter of natural gas (L-water/m3

–natural gas) 

for drilling and hydraulic water fracturing of four major shale 

gas plays (Haynesville, Marcellus, Barnett, and Fayetteville; 

fig. 4.); in addition, up to 0.3 L of water may be needed for 

processing each cubic meter of natural gas in order to remove 

gas liquids, mercury, hydrogen sulfide, and other impurities (Mantell, 2010). These estimates are consistent with the 

range in water consumption provided by the International 

Energy Agency (2012b) (table 1). Coalbed natural gas, though 

considered an unconventional resource, often does not require 

hydraulic fracturing for its extraction, so water requirements 

for producing coalbed natural gas are generally less than those 

for other unconventional gas reservoirs. 

Table 1. Water consumption for different steps in production of natural gas, oil, coal, and uranium.

[--, no data; EOR, enhanced oil recovery]

Hydraulic fracturing Processing/refining Total production

Natural gas, in liters of water per cubic meter of gas

Conventional -- 5

0.3 10.004–0.04

Conventional with fracturing -- 5

0.3 10.02–0.19

Tight gas 5

0.1–0.2 50.3 10.04–0.38

Shale gas 5

0.1–0.2 50.3 10.08–3.8

Oil, in liters of water per liter of oil

Conventional -- 1,20.19–1.4 1

0.04–1.9

Conventional with fracturing -- 1,20.19–1.4 1

0.19–1.9

Conventional—primary -- 1,20.19–1.4 1

0.2

Conventional—secondary -- 1,20.19–1.4 2

8.6

Conventional—EOR -- 1,20.19–1.4 2,31.9–13

Tight oil -- 1,20.19–1.4 1

0.19–3.8

Shale oil -- 1,20.19–1.4 --

Oil sands -- 1,20.19–1.4 4

0.4–5.8

Oil shale -- 1,20.19–1.4 6

0. 8–11.8

Coal, in liters of water per metric ton of coal

Conventional surface/underground -- -- 3,7,875–500

Uranium, in liters or water per kilogram of enriched uranium

Conventional -- 3,99,600–16,500 3,99,600–16,500

Solution mining -- 3,951,600–56,500 3,951,600–56,500

1

International Energy Agency (2012b).

2

Wu and others (2009); Wu and Chiu (2011).

3

Gleick (1994).

4

Moorhouse and others (2010).

5

Mantell (2010).

6

U.S. Government Accountability Office (2010).

7

Pate and others (2007).

8

Nicot and others (2011).

9

Mudd and Diesendorf (2008).

Continued on page 15
10 The Water-Energy Nexus—An Earth Science Perspective

Water Availability and Usage in the United States

Water Availability

Water availability is a somewhat nebulous 

term. The water volume within a hydrologic system and 

the rates of water movement through that system can be 

measured or estimated (albeit with some degree of uncertainty). Such quantification is integral to the concept of 

water availability, but the concept extends beyond merely 

knowing volumes and rates of water flow. The amount of 

water that is available for a particular use is dependent on 

many other factors—including the quality of the water; 

the intended use of the water; laws and regulations that 

govern water ownership and use; the physical nature of the 

hydrologic system; the ecosystems, culture, lifestyles, and 

societal values of the region; and the economic aspects of 

water development—and these factors vary from region 

to region. They also vary over time as economic, climatic, 

hydrologic, and environmental conditions change. As such, 

water availability is best determined on a region-by-region 

basis with periodic reassessments over time. As of 2014, 

no quantitative assessment of water availability has been 

completed at the national level, though such assessments at 

the state and watershed level are common and are often key 

components of water-management strategies. As directed 

by the United States Congress, the U.S. Geological Survey 

is currently (2014) working with other Federal and State 

agencies to conduct a nation-wide water census that will 

provide an assessment of the status and trends in freshwater 

availability and use (Alley and others, 2013). 

where 

P is precipitation, 

Qin is surface and subsurface flow into the 

watershed, 

ET is evapotranspirzation, 

ΔS is change in water storage, and

Qout is surface and subsurface flow out of the 

Quantification of 

water resources is commonly done in the context 

of a hydrologic or water 

budget (Healy and others, 

2007). A water budget 

describes the movement 

of water into, through, and 

out of a representative volume, such as a watershed, 

a state, or the country as 

whole. A simple waterbudget equation for a 

watershed is given by:

P + Qin = ET + ΔS + Qout,

watershed (including human withdrawals).

The equation states that water entering the watershed (through 

precipitation or surface and subsurface flow) is lost to evapotranspiration, flows out of the volume, or adds to water storage 

in the watershed (fig. B–1). 

Although it is difficult to quantify, water storage is a key 

metric for determining sustainable water use—continuous 

decreases in water storage will eventually result in decreased 

availability for humans and the environment. Surface features such as lakes, wetlands, and to a lesser extent rivers and 

streams are the most prominent visual expressions of water 

storage; however, the vast majority of freshwater in the United 

States is found in the subsurface soil water and groundwater 

(Healy and others, 2007). Accurate assessment of subsurface 

water resources is one of the more challenging aspects of 

efforts to quantify available water.

Precipitation

Surface-water inflow,

imported water

(pipelines, canals)

Groundwater

inflow

Surface-water outflow,

exported water

(pipelines, canals)

Groundwater outflow

Aquifer

Evapotranspiration

Bedrock

Water table

Unsaturated zone

Figure B–1. A watershed showing 

components of a water-budget 

equation. (Healy and others, 2007)
0

Less than 10

10 to 20

20 to 30

30 to 41

41 to 50

50 to 61

178 to 203

203 to 254

254 to 305

305 to 356

356 to 406

Greater than 406

EXPLANATION

Annual precipitation, in centimeters

61 to 71

71 to 81

81 to 91

91 to 102

102 to 127

127 to 152

152 to 178

Figure B–2. Average annual precipitation in the conterminous 

United States, 1981–2010, as determined with the PRISM dataset

(http://prism.oregonstate.edu/normal/, PRISM Climate Group, 

Oregon State University).

Total withdrawals

Public supply

Rural domestic and livestock

Irrigation

Thermoelectric power

Other

EXPLANATION

0

200

400

600

800

1,000

1,200

1,400

1,600

1,800

1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010

Year

Withdrawals, in billion liters per day

Water in Energy Production and Use 11

Figure B–3. Trends in water 

withdrawal by water-use 

category, 1950–2010. “Other” 

includes industrial, aquaculture, 

and mining. (Maupin and others, 

2014)

With an average annual precipitation of 767 mm, the 

United States is often thought to have an abundance of freshwater, but water is not evenly distributed across the country. 

Annual rates of precipitation range from less than 100 mm in 

Death Valley, California, to more than 7,000 mm in parts of 

Hawaii and the Olympic Peninsula of Washington (fig. B–2). 

Vast regions of the western United States have arid or semiarid climates; these regions also hold substantial fossil-fuel 

resources. Conflicts among water users are woven throughout 

the history of these western regions. Competition for limited 

water supplies in these regions will likely increase with growing populations and increased demands for energy.

Water Use

Clarification of terminology used in this report will 

help to avoid ambiguity and confusion. Water withdrawal is 

defined as water removed from the ground or diverted from a 

surface-water source for use. Water use refers to withdrawal 

of water for a specific purpose (for example, water supply 

or irrigation). Water consumption (sometimes referred to 

as consumptive use) is that part of withdrawn water that is 

evaporated, transpired, incorporated into products or crops, 

consumed by humans or livestock, or otherwise removed from 

the immediate water environment. Depending on category of 

water use, consumption might be a large percentage of withdrawal, as with irrigation, for example, or only a small part 

of withdrawal, as with thermoelectric power plants that use 

once-through cooling systems. Most of the water withdrawn 

for irrigation is transferred to the atmosphere through evapotranspiration. In once-through cooling systems, most of the 

water withdrawn for cooling is returned to the original supply 

source; power plants with these systems withdraw large volumes of water, but they usually consume only small amounts 

of that water. Nonconsumptive water use, however, can still 

affect water availability—any human activity, including the 

development of energy resources, has the potential to degrade 

water quality, thereby reducing the amount of freshwater 

available for other uses. 

Quantifying water usage in the United States is a difficult 

task, but it is a more tractable endeavor than quantifying water 

availability. The U.S. Geological Survey publishes estimates 

of water withdrawal for the Nation on a 5-year cycle for 

8 categories of water use: public supply, rural domestic supply, irrigation, livestock, industrial, aquaculture, mining, and 

thermoelectric power. Thermoelectric power plants withdraw 

the largest share of water, followed by irrigation, and public 

water supply (fig. B–3).
12 The Water-Energy Nexus—An Earth Science Perspective

Hydraulic Fracturing

Hydraulic fracturing, or “fracking”—few terms 

arouse as much passion on the part of the public 

and energy developers. To many, the term signals the 

destruction of pristine aquifers that supply drinking water 

to more than half of the population of the United States. 

Others cheer the facts that hydraulic fracturing and related 

advances in well drilling have led to improved national 

energy security and reduced energy costs. So what is the 

reality of the situation? The truth is that there are many 

issues to consider. In this section, we briefly describe the 

process of hydraulic fracturing, highlight the benefits it provides, and discuss its potential unintended consequences in 

regard to water resources.

In many parts of the United States, natural gas and 

oil exist in low-permeability rocks such as shales and tight 

sandstones. Until recently, extraction of these resources 

has not been economically feasible because of that low 

permeability. The process of hydraulic fracturing involves 

injection of fluids into a well under pressures high enough 

to fracture the host rock, thereby increasing the permeability of the rock and facilitating the extraction of the 

hydrocarbon resource. Hydraulic fracturing, technologies 

such as directional drilling, which can align a well parallel 

to reservoir dip (fig. C–1), and drill rigs that can efficiently 

drill multiple wells from a single drill pad all have substantially enhanced the ability to develop low-permeability 

hydrocarbon reservoirs. As a result, annual estimates of 

U.S. natural gas reserves have risen dramatically since the 

mid-1990s (fig. C–2).

Fracturing of reservoirs has been used for decades to 

enhance productivity of oil, gas, and even drinking water 

wells. Various fluid mixtures can be used in the procedure. The 

most commonly used fracturing fluids for gas and oil wells 

in shales and tight sands are referred to as slickwater fluids; 

water, gels, foams, propane, and kerosene have also been used 

as fracturing fluids. Slickwater consists of about 87 percent 

water, 11 percent sand, and 2 percent chemical additives 

(fig. C–3; Groundwater Protection Council and ALL Consulting, 2009; National Energy Technology Laboratory, 2013). 

Sand or ceramic beads are added to prop fractures open, and 

the chemical additives are designed to facilitate flow from the 

reservoir by reducing friction and inhibiting the formation of 

scale and microbial films. Additives can include acids, surfactants, biocides, and friction reducers (fig. C–3).

Hydrocarbon-rich shale unit

Shallow 

Groundwater

Shallow 

hydrocarbon-bearing

units

Zone of

hydraulic fracturing

Figure C–1. Cross-section view of a hydraulically fractured 

shale gas well. (Modified from Soeder and Kappel, 2009)

Annual estimates of natural gas reserves in

the United States, in trillions of cubic meters 

Year

4

5

6

7

8

9

10

1980 1985 1990 1995 2000 2005 2010 2015

Figure C–2. Annual estimates of natural gas reserves in the 

United States, 1980–2012. Estimated reserves have nearly doubled 

since the mid-1990s, largely because techniques like hydraulic 

fracturing allow gas to be captured from new unconventional 

reservoirs. (U.S. Energy Information Administration, 2013c)

Demonstrators rallying against fracking.
Slurry guar

Petroleum distillate

Clay

Surfactant

Crosslinker

Potassium hydroxide

Boric acid

Breaker

Cured resin

Non-emulsifier surfactant

 Scale inhibitor

Polyphosphoric acids

Surfactant

Glycolic acid

Methoxyacetic acid

Ethylene glycol monobutyl ether

Isopropyl alcohol

Dodecylbenzenesulfonic acid

Glacial acetic acid

Concentrated hydrochloric acid

EXPLANATION

Water (88 percent)

Additives (2 percent) Sand

(11 percent)

A

B

Water in Energy Production and Use 13

Figure C–3. Relative volume of the various materials used 

to hydraulically fracture an oil well in the Texas portion of the 

Permian Basin, from a total volume of 4.5 million liters (data from 

fracfocus.org). A, Relative volumes of water, sand, and additives 

used. B, relative volume of the specific additives used.

The fluid mixture is injected into the reservoir under 

pressures that exceed the strength of the host rock, producing a 

series of fractures in that rock. After a period of time, ranging 

from hours to weeks, pressure is removed from the system, 

and extraction of hydrocarbon product begins. Hydraulic fracturing commonly consists of a series of stimulations over different intervals of the well, with the process usually initiating 

at the far end of a well and stimulations gradually progressing 

back up the well (Groundwater Protection Council and All 

Consulting, 2009). The volume of water required for hydraulic fracturing is highly variable and depends on the hydraulic 

properties of the reservoir, the dimensions of the well, and the 

specific techniques applied. Median values of water use in the 

Barnett, Haynesville, and Eagle Ford Shales in Texas were 

estimated at 9,500–14,000 L per meter of linear distance of 

fractured well casing (Nicot and Scanlon, 2012). Accordingly, 

the hydraulic fracturing of a 3,500-m-long horizontal well 

could require up to 49 million L of water. 

Upon completion of the fracturing procedure, pumping 

is initiated to extract the hydrocarbons. Water is also extracted 

with the hydrocarbons. Some of this produced water is injection water and some is native formation water. The produced 

water can be reused in some cases; otherwise, the water is 

typically disposed of by deep subsurface injection or by delivery to a water-treatment plant. A large portion, in some cases 

in excess of 90 percent, of the injected fluid is never recovered 

from the reservoir. This is particularly true for shale-rich units 

(Groundwater Protection Council and ALL Consulting, 2009; 

National Energy Technology Laboratory, 2013). In addition to 

water retained in the artificially developed fractures, water is 

often lost to the reservoir through a process called imbibition, 

in which injected fluids replace hydrocarbons that were originally stored in very small pores in the reservoir rock. Shales 

typically have a much larger percentage of these very small 

pores than do sandstones, which might explain the relatively 

higher water loss noted for wells in shale relative to those in 

sandstone (Byrnes, 2011).

Most public concerns regarding hydraulic fracturing are 

centered on three issues: contamination of streams and shallow 

freshwater aquifers, the disposition of produced waters, and 

the potential for inducing earthquakes or other seismic activities. These issues are addressed individually in the following 

paragraphs.

Streams and shallow aquifers can be contaminated by 

liquid spills or leaks that occur on the land surface; spilled 

contaminants can include drilling fluids, fracturing fluids, and 

fuels used by machinery involved in well drilling and development (Kappel and others, 2013). Streams and ecosystems 

can also be adversely affected by sediment released during 

the construction of roads and pipelines that are needed for 

new wells. Surface contamination is not specific to wells that 

undergo hydraulic fracturing; it is a concern with all oil and 

natural-gas operations. Shallow aquifers also can be affected if 

hydrocarbons, fracturing fluids, or deep brines are transported 

upward from the hydrocarbon reservoir. Shallow aquifers and 

deep reservoirs are typically separated by hundreds or thousands of meters of low-permeability rocks that serve as a natural barrier to that transport (fig. C–4). The composite thickness 

and permeability of these intervening rocks and the differences in fluid pressures between the shallow and deep systems 

govern fluid movement. The permeability of these “confining” 

layers could potentially be enhanced by the fracturing procedure; however, after analyzing data from thousands of hydraulic fracturing operations in the Marcellus, Barnett, Woodford, 

Eagle Ford, and Niobrara Shales, Davies and others (2012) 

concluded that the probability of a stimulated fracture extending more than 350 m was very low, about 1 percent. The maximum height of fractures measured in that study was 588 m; 

the minimum depth interval between the bottom of shallow 
EXPLANATION

Barnett

Fayetteville

Haynesville

Marcellus

Woodford

Antrim

New Albany

Utica

Eagle Ford

0

1,000

2,000

3,000

4,000

5,000

Depth below ground surface, in meters

Approximate zone of fresh groundwater

Approximate pay zone of shale resource

Shale play location

14 The Water-Energy Nexus—An Earth Science Perspective

freshwater aquifers and the top of the fractured zone 

was about 800 m for these systems. In a separate 

study, Jackson and others (2013) suggested that the 

contamination of shallow aquifers by fluid movement 

upward through fractures created by hydraulic fracturing 

has a low probability. As of 2013, no confirmed cases of 

such aquifer contamination have been documented in the 

United States; however, cases of suspected contamination 

are being investigated in Texas, Wyoming, and Pennsylvania (U.S. Environmental Protection Agency, 2011b). 

Compromised well casings, such as those inadequately 

sealed with cement grout, can also serve as avenues for the 

migration of methane and saline water to shallow aquifers 

(Ide and others, 2006); as with surface contamination, this 

is a concern for all oil and natural gas wells.

The treatment of produced waters can be problematic, 

both in terms of water quantity and quality. In addition to 

the chemicals added to fracturing fluids, naturally occurring 

contaminants in the deep reservoir can be mobilized and 

dissolved in these fluids. These contaminants can include 

radium-226 and radium-228 as well as multiple volatile 

organic compounds and salts. Municipal wastewater treatment plants were not originally designed to treat large 

volumes of saline fluids. Some plants in rural Pennsylvania, 

for example, were completely overwhelmed. As a result, 

private facilities were established specifically for treating produced water, and the reuse of produced water was 

expanded (Schmidt, 2013). 

Hydraulic fracturing can induce small earthquakes 

of moment magnitude less than 1, but according to recent 

reports, hydraulic fracturing does not pose a high risk 

for inducing seismic activities that can be felt (National 

Research Council, 2012; Ellsworth, 2013). (“Felt” earthquakes are typically those with magnitudes of 2 or greater.) 

From 2005 through 2012, thousands of wells were hydraulically fractured in Pennsylvania, but only 6 earthquakes 

with magnitudes of 2 or greater were detected within the 

Figure C–4. Approximate depth of zones of shallow, fresh 

groundwater sources (blue) relative to reservoir depths for 

important shale gas reservoirs (green) of the United States. 

Deeper shales, such as the Haynesville and Woodford, have 

a greater natural buffer for restricting fluid migration upward. 

Locations of gas reservoirs are shown in figure 4. (Data from 

National Energy Technology Laboratory, 2013)

Hydraulic Fracturing—Continued

footprint of the Marcellus Shale (Ellsworth, 2013), the largest 

having a magnitude of 2.3. A magnitude 2.9 earthquake in 

south central Oklahoma might have been related to hydraulic 

fracturing, but seismic data were insufficient to conclusively 

rule out other causes. Injection of wastewater is a more 

common cause of felt earthquakes than hydraulic fracturing 

(see Box H—Subsurface Fluid Injection), although injectioninduced earthquakes are still rare (Ellsworth, 2013).

Bakken drilling and completion activities 

at a well along Interstate-94, 6 miles east 

of Belfield, North Dakota, 2013.
0

10

20

30

40

50

60

70

1930 1940 1950 1960 1970 1980 1990 2000

Million liters per day (oil and water) or 

million cubic meters per day (carbon dioxide)

Year

EXPLANATION

Oil produced

Water injected

Water produced

Carbon dioxide (CO2

) injected

Water in Energy Production and Use 15

Increased natural gas production from shale and other 

tight reservoirs in recent years has led to concerns over 

water availability. Nicot and Scanlon (2012) estimated that 

net water use for hydraulic fracturing of tight-gas and shalegas reservoirs in Texas would increase from 46 billion liters 

of water per year (L/yr) in 2012 to 179 billion L/yr by the 

mid-2020s. At the same time, operators are expanding their 

reuse of produced waters and other wastewaters to minimize 

freshwater use (Curtright and Giglio, 2012). Increased reuse 

and recycling of water and increased use of saline water and 

oil-based fluids for drilling and hydraulic fracturing may help 

offset the higher water demand of important unconventional 

gas resources. 

Oil

Water requirements for exploration, drilling, and primary 

production of conventional oil wells are similar to those for 

conventional natural gas wells. During primary production, 

reservoir pressures facilitate movement of oil up the well 

bore, and water use is minimal. With time, however, reservoir 

pressures decline; to enhance productivity, injection wells 

are drilled across the field to pump water into the formation to drive hydrocarbons to producing wells. This process, 

referred to as secondary production or water flooding, has 

higher water-use rates (fig. 5), up to about 8.6 liters of water 

per liter of oil (L-water/L-oil) (Wu and others, 2011), although 

produced or other non-freshwaters are often used in secondary 

production. With time, water flooding becomes less effective, as the oil remaining in the reservoir is typically trapped 

in small isolated pockets. A range of tertiary or enhanced oil 

recovery techniques can then be employed to extract a portion 

of the remaining product. Estimated rates of water consumption for enhanced recovery vary from 1.9 L-water/L-oil for 

forward combustion/air injection up to 13 L-water/L-oil for 

carbon dioxide (CO2

) injection (Gleick, 1994; Wu and others, 

2011). Given current interest in carbon capture and storage, 

CO2

 injection is the fastest growing category of enhanced 

recovery in the United States (National Energy Technology 

Laboratory, 2010). As with secondary production, much of 

the water needs for enhanced recovery can be met by use of 

recycled, produced, or other non-freshwaters.

As with natural gas, development of unconventional shale 

and tight oil reservoirs typically requires more water than that 

required for primary production of conventional oil reservoirs 

(table 1). The higher water requirements are largely due to the 

water needed for hydraulic fracturing. Hydraulic fracturing 

of a well in units such as the Eagle Ford Shale in Texas can 

require upwards of 50 million L of water (Nicot and others, 

2011). 

Oil sands are bitumen-bearing, poorly consolidated sediments that constitute a large oil resource for North America. 

The largest continental source of oil sands is the Athabasca 

Tar Sands in Alberta, Canada. Oil sands are a relatively small 

energy source in the United States (U.S. Bureau of Land 

Management, 2012), but approximately 112 billion L of oil 

were produced from oil sands in Canada in 2012 (Alberta 

Government, 2013), accounting for more than 50 percent 

of that country’s oil production. Data from the Province of 

Alberta indicate that water requirements for the development 

of oil sands are similar to those for the development of tight 

Figure 5. Oil and water production and water and CO2 injection as part of primary, secondary, and tertiary production periods for the 

Denver Unit of the Wasson Field, west Texas, 1938–1988, with enhanced oil recovery (EOR) during tertiary production indicated. (From 

National Energy Technology Laboratory, 2010)

Continued on page 17
ATLANTIC

OCEAN

LAKE

MICHIGAN

LAKE

HURON

LAKE ERIE

LAKE ONTARIO

Study area

EXPLANATION

Appalachian Basin Province 

Western Margin Marcellus AU

Foldbelt Marcellus AU

Interior Marcellus AU

0 100 200 MILES

0 100 200 KILOMETERS

45° N

43° N

41° N

39° N

37° N

35° N

33° N

89° W 87° W 85° W 83° W 81° W 79° W 77° W 75° W 73° W 71° W

GA

SC

NC

VA

PA

IL IN OH

MI WI

WV

MD

DE

NJ

NY

MA

VT

NH

CT RI

AL

MS

TN

KY

16 The Water-Energy Nexus—An Earth Science Perspective

The Marcellus Shale—A Vast Energy Resource with Important 

Challenges

The Marcellus Shale is a Middle Devonian siliciclastic black shale that extends along a large portion of the 

Appalachian Basin Province (fig. D–1) at depths of up to 

2,000 m below land surface. It holds immense quantities 

of natural gas; the median estimated undiscovered, recoverable gas is about 2.38 trillion m3

 (Coleman and others, 

2011), making the Marcellus one of the largest shale gas 

resources in the United States. The first Marcellus Shale 

gas well went into production in 2005, producing 0.16 million m3

 of gas in the first month (Carter and others, 2011). 

Since that time, oil and gas production from the Marcellus Shale has grown rapidly. In 2012, 2,246 permits were 

issued for unconventional oil and gas wells in Pennsylvania 

alone (Pennsylvania Department of Environmental Protection, 2012).

The rapid development of natural gas in the region 

comes with a number of tradeoffs and challenges. The 

energy boom has led to greater national energy security and 

Figure D–1. Map showing the extent of the Appalachian Basin Province and the three assessment units (AUs) of the Marcellus 

Shale used in its resource assessment. (Coleman and others, 2011)

lower energy prices for the consumer and has also generated 

numerous new jobs in a region hit hard by the recession of 

2008. There are, however, a number of potentially adverse 

consequences are associated with the energy development, 

including altered lifestyles, overloaded public infrastructure, 

and deterioration in quality of water, land, air, and ecosystem 

resources (Kappel and others, 2013). Land clearing for drilling 

pads, pipelines, compressor stations, and new roads can substantially alter landscapes, promoting increased soil erosion 

that can lead to contamination of streams and choking of ecosystems. Heavy traffic can damage existing roads and contribute to air pollution and traffic congestion. Hydraulic fracturing 

raises concerns among many people in regard to water supply 

and contamination (see Box C—Hydraulic Fracturing). Defective or improperly constructed retention ponds, pipelines, and 

wells can lead to unintended releases of hydrocarbons and 

produced waters and the contamination of surface water and 

groundwater.
Water in Energy Production and Use 17

oil wells (table 1). The water needed for oil sands development is extracted within a relatively small area; the effect of 

those large extractions on other local water users is as of yet 

unknown. Saline groundwater and recycled process waters 

can be used in place of freshwater in some oil-sand operations 

(Alberta Government, 2013). 

Oil shale consists of kerogen-rich shale and fine-grained 

sedimentary rocks from which oil can be extracted by heating. 

There are no commercial oil-shale developments currently 

(2014) in operation in the United States, but oil shale is a 

potential energy source for the future. Oil shale can be mined 

and transported to a surface facility to be processed, or it can 

be processed in place. In-place production involves heating 

the shale in the ground to release the hydrocarbons and allow 

them to flow to collection systems (U.S. Bureau of Land 

Management, 2012). Preliminary estimates indicate that water 

consumption rates for the development of oil shale may not be 

substantially greater than those for secondary development or 

enhanced oil recovery of a traditional oil well (table 1). The 

Green River Formation, found throughout portions of Wyoming, Colorado, and Utah, is the largest oil-shale resource in 

the world, holding an estimated 424 trillion L of oil in place 

(Johnson and others, 2009; Johnson and others, 2010). It is 

located in areas of arid and semiarid climates where water 

resources are scarce; the rate at which oil can be produced 

from the formation might ultimately be determined by the 

availability of water. 

Crude oil undergoes several chemical processes at refineries in order to create usable end products such as gasoline, 

diesel fuel, and jet fuel. Water is required in a number of 

these processes, primarily for cooling and condensing both 

steam and end products after chemical reactions. Water that 

is withdrawn for cooling, however, is not always consumed; 

refineries recycle and reuse much of their cooling water. The 

exact refinery processes vary with the form of the crude oil 

and end product, but estimated water requirements vary little. 

Refineries need ready access to large supplies of water. Estimated water consumption at refineries is about 1.4 L of water 

per L of end product (Wu and others, 2011). On a daily basis 

in 2013, U.S. refineries processed about 3 billion L of crude 

oil (U.S. Energy Information Administration, 2014b), and in 

so doing consumed about 4.2 billion L of water. If the largest 

refinery in the country, in Baytown, Texas, operated at its full 

capacity of 90 million L of oil per day, it would consume on 

the order of 125 million L of water daily, equivalent to about 

13 percent of the average daily amount of wastewater treated 

in nearby Houston (City of Houston, 2013). 

Water Quality

Infrastructure and Development Practices

Infrastructure and practices used in oil and gas production 

have the potential to produce unintended environmental consequences. Under natural conditions, subsurface reservoirs are 

isolated from each other by low-permeability geologic layers 

or seals, such as shales and mudstones, which prevent vertical migration or mixing of fluids contained in the reservoirs. 

These natural barriers are one reason why shallow groundwater can remain relatively fresh despite being underlain by 

saline brines and large hydrocarbon accumulations (fig. 2). 

Perforation of geologic seals by oil and gas wells provides 

potential pathways for fluids to move from one reservoir to 

another, but modern oil and gas wells are designed in such 

a way as to prevent this from happening. Typically, multiple casings are installed at each well to prevent unintended 

fluid movement between reservoirs (fig. 6). Cement grout is 

injected into portions of the annulus between the casings and 

between the outermost casing and the surrounding formation 

as a seal. Tests are conducted according to regulatory and best 

industry guidelines to ensure fidelity of the wellbore and integrity of the cement grout (Hetrick, 2011). Despite caution and 

testing, the integrity of the casing and grout can be inadequate 

or deteriorate with time, and the potential exists for pathways 

to develop along the wellbore that would permit migration 

of natural gas, oil, formation fluids, and injected fluids. Of 

particular concern is the migration of fluids in the annulus 

between the outermost casing and the adjacent formation 

(Mordick, 2011). Unintended or stray migration of natural gas 

along production wellbores has been a chronic problem for the 

oil and gas industry (Stein and others, 2003). Bexte and others 

(2008) showed that when very careful grouting procedures 

The term salinity refers to the amount of salt in a given water sample; 

it is usually is expressed in terms of total dissolved solids (TDS). 

Water with a TDS concentration greater than 1,000 mg/L commonly is 

considered saline. This somewhat arbitrary upper limit of freshwater 

is based on the suitability of water for human consumption. Water 

with a TDS concentration greater than 1,000 mg/L is used in some 

areas, but water containing more than 3,000 mg/L is generally too 

salty to drink. The term “brackish” is sometimes used to describe 

water with TDS greater than 1,000 mg/L but less than 10,000 mg/L. 

Water with salinity greater than seawater (about 35,000 mg/L) is 

referred to as brine.

Continued on page 19
MT

CANADA

WY

SD

ND

Fargo

Minot

Pierre

Bismarck

Sheridan

Dickinson Jamestown

Williston

Rapid City

Grand Forks

Glendive

Miles

City 

Sidney

108° 107° 106° 105° 104° 103° 102° 101° 100° 99° 98° 97°

49°

48°

47°

46°

45°

44°

CANADA

UNITED STATES

NORTH DAKOTA

MONTANA

SOUTH DAKOTA

WYOMING

POPLAR

DOME

CEDAR CREEK

 CENTRAL 

MONTANA

 UPLIFT

ANTICLINE

BILLINGS

ANTICLINE

LITTLE KNIFE

ANTICLINE

NESSON

ANTICLINE

Bakken-Lodgepole 

Total Petroleum

System

Williston Basin 

Province boundary

0 50 100 KILOMETERS

0 50 100 MILES

Powder River

Basin boundary 

18 The Water-Energy Nexus—An Earth Science Perspective

The Powder River Basin and the Williston 

Basin are adjacent structural basins within the Great 

Plains Physiographic Region (fig. E–1). Both basins 

have a semiarid climate, and both have been important 

sources for energy resources since at least the middle 

1900s. The implementation of newer technologies for 

recovering fossil fuels has led to increased rates of development in both basins; however, different fuels and different 

practices between the basins have led to something of a 

conundrum—a large surplus of water in one basin and a 

substantial shortage of water in the other.

The Powder River Basin covers an area of about 

61,000 km2 in northern Wyoming and southern Montana. 

The basin is an important source of coal, oil, and natural 

gas. Coalbed natural gas development has expanded rapidly 

throughout the basin since the late 1990s; between 2000 

and 2010, more than 59,000 well-drilling permits were 

approved in Wyoming (Wyoming Oil and Gas Conservation Commission, 2011). Natural gas is captured by withdrawing water from coalbeds; lowering the water pressure 

releases the gas.

About 85 billion L of water were produced annually 

in the Wyoming portion of the basin between 2002 and 

2013 (fig. E–2). The produced waters are fresh to moderately saline (dissolved solids concentration in the range 

of 200–4,000 mg/L), but they have high proportions of 

sodium relative to calcium and magnesium, thus rendering 

A Tale of Two Basins—Water Surplus/Water Deficit

the waters unsuitable for irrigation without treatment. A range 

of disposal options have been utilized, including storage in 

infiltration impoundments, treatment for irrigation or for 

release to streams, and reinjection into the subsurface (Bern 

and others, 2013a). The cost of these options and the possibility of adverse environmental consequences raise questions 

about the continued viability of coalbed natural gas development in the Powder River Basin. 

The Williston Basin encompasses approximately 

365,000 km2 in eastern Montana, western South and North 

Dakota, and southern Saskatchewan. Oil was first discovered 

in the basin in the 1920s, and large-scale production began 

in the 1950s. A peak in oil production occurred in 1986, and 

production tapered off until the early 2000s (fig. E–3) when 

new techniques allowed oil reserves in the Bakken Formation 

to be tapped. Estimates of recoverable oil exceed 1 trillion L, 

making the Williston one of the largest oil-producing areas in 

North America.

Oil recovery from the Bakken Formation is economically 

feasible only because of recent improvements in directional 

drilling and hydraulic fracturing. A typical well in the Bakken 

Formation is drilled to a depth of about 3 km; the drill hole is 

then extended laterally within the formation for a distance of 

about 3 km. Hydraulic fracturing is used to increase permeability in the vicinity of the drill hole so that oil will flow more 

freely to the well. The fracturing is done incrementally over 

the length of the horizontal section of the well, requiring an 

Figure E–1. Map showing Powder River Basin and Williston Basin.

average of about 10 million L of 

water for each well (Scanlon and 

others, 2014).

The number of wells drilled 

in the North Dakota portion of the 

Bakken Formation is projected to 

be about 2,000 per year (Lymn, 

2014). This equates to approximately 20–40 billion L of water 

per year, much less than the annual 

excess produced water in the Wyoming portion of the Powder River 

Basin. Water is a limited resource 

in western North Dakota, and 

most available water was long ago 

allocated for existing agricultural, 

industrial, and municipal interests. 

Water for well development must be 

obtained from entities that currently 

own water rights. As more and 

more wells are drilled, the demand 

(and the price) for water will only 

increase.
0

20

40

60

80

100

120

2000 2014

Water production, in billions of liters

Year

2002 2004 2006 2008 2010 2012

0

10

20

30

40

50

60

1950 2020

Oil production, in billions of liters

Year

1960 1970 1980 1990 2000 2010

Conductor

casing

Surface

casing

Intermediate

casing(s)

Cement

Gas-bearing shale

Production

casing Hydrocarbon

reservoir

Geologic seal

Fresh 

groundwater

Geologic seal

Zone of formation brine Zone of brackish groundwater

Production

tubing

Not to scale

Water in Energy Production and Use 19

Figure E–2. Water production for coalbed natural gas in the 

Powder River Basin, Wyoming, 2002–2013. (Wyoming Oil and Gas 

Conservation Commission, 2014)

Figure E–3. Annual oil production in North Dakota, primarily from 

the Williston Basin, 1950–2013. (Data from North Dakota Oil and 

Gas Division, 2014)

So why not use Wyoming’s produced water for well 

development in Montana and North Dakota? The answer is 

mainly one of economics. Water is expensive to transport 

unless natural stream channels can be used. The high sodium 

concentration of the produced water makes it inappropriate 

for direct discharge to streams because of concerns related to 

stream ecology and downstream irrigators. Alternative transport options such as truck and rail lines or the construction of 

a dedicated water pipeline are currently (2014) nonviable.

are used, natural gas movement along casings occurred 

in about 1 percent of newly installed horizontal wells in 

Alberta, Canada.

Oil and gas wells are abandoned when the resource 

has been depleted or it is not economically practical to 

continue resource extraction. Abandoned wells, if not 

properly sealed, can serve as conduits for the contamination of freshwater aquifers. Extended lengths of oil and 

gas wells can be uncased and thus open to many different 

geologic units and aquifers. If one of those geologic units 

becomes a target for nearby operations, such as hydraulic 

fracturing or wastewater injection, then the injected fluids 

could potentially be transported through the abandoned 

well to a freshwater aquifer. State laws require that oil 

Figure 6. A modern vertical oil or gas well (based on Teodoriu 

and Falcone, 2008). The cement seal may not extend over the 

entire vertical extent of a well. Some States require isolation of 

only freshwater and gas-producing zones. 

Continued on page 21
20 The Water-Energy Nexus—An Earth Science Perspective

Gasoline Additives—Clean Air vs Clean Water? The MTBE Story

MTBE (methyl tertiary butyl ether) was first 

introduced into gasoline in 1979 as an octane enhancer. 

It replaced the tetraethyl lead that was being phasedout because of concerns about lead in the environment 

(U.S. Environmental Protection Agency, 1999). Use of 

MTBE expanded with passage of the Clean Air Act amendments of 1990, which required that areas with severe 

ozone-smog problems use reformulated gasoline that 

includes an “oxygenate.” Oxygenates are compounds that 

contain oxygen and when added to gasoline improve combustion and reduce harmful motor vehicle emissions. 

By the late 1990s, MTBE made up 3 to 5 percent of 

the national gasoline supply. From 1993 to 1998, it was 

the second most produced organic chemical in the United 

States (Moran and others, 2004). Also at this time, MTBE 

started showing up in groundwater and in some reservoirs 

and rivers used as public water supplies (U.S. Environmental Protection Agency, 1999). Apparently, in trying to solve 

an air pollution problem, a water contamination problem 

was created.

Its physical properties make MTBE a prominent 

groundwater contaminant. It dissolves easily in water and 

does not tend to become affixed to soil and aquifer material, 

thus moving as quickly as water through the subsurface. It 

is also slow to biodegrade and can persist longer in groundwater than many other organic compounds, including 

other components of gasoline, such as benzene and toluene 

(Zogorski and others, 2006). There are numerous potential 

sources of MTBE in groundwater, including leaking storage 

tanks, leaks and accidents during transport, homeowner gasoline spills, stormwater runoff, and even precipitation scavenging MTBE in the air. 

The U.S. Environmental Protection Agency (EPA) 

considers MTBE a possible carcinogen, although the human 

health effects have not been clearly established (U.S. Environmental Protection Agency, 1999). What really brought 

MTBE to the forefront was that even very low concentrations of MTBE make water taste and smell “foul and nasty,” 

like turpentine. In 1997, EPA issued a drinking water advisory indicating that MTBE concentrations in drinking water 

below the range of 20–40 parts per billion (ppb) will likely 

avert unpleasant taste and odor effects, although some people 

can detect the chemical at concentrations as low as 1 ppb 

(U.S. Environmental Protection Agency, 1999). The lower 

threshold of 20 ppb also was considered to be protective of 

human health while further studies of the risks were underway. 

The first major MTBE groundwater contamination 

incident occurred in Santa Monica, California. In 1996, the 

city discovered that two of its drinking water well fields were 

contaminated with high levels of MTBE (U.S. Water News 

Online, 1996). The two well fields, representing half of the 

city’s drinking water supply, were shut down and the city 

was forced to purchase replacement water until the groundwater supply was restored with a treatment system in 2010. 

(Shorney-Darby and others, 2011). 

Low concentrations of MTBE have been detected in 

groundwater nationwide, particularly in the highly populated New England and Mid-Atlantic States where MTBE 

Smog attributed to motor vehicle emissions was common in many metropolitan areas of 

the United States prior to the implementation of Federal and State gasoline programs.
High MTBE-use area

MTBE concentration, in micrograms per liter

EXPLANATION

No detection or less than 0.2

0.2 or greater

HAWAII

ALASKA

Oahu

Water in Energy Production and Use 21

use was high (fig. F–1). Despite its relatively short history of 

use, MTBE was the second most frequently detected volatile 

organic compound in a national survey of drinking-water wells 

(after chloroform) (Zogorski and others, 2006). It was detected 

in about 5 to 10 percent of community drinking water supplies 

in high oxygenate use areas, but concentrations were generally 

less than 1 ppb (U.S. Environmental Protection Agency, 1999). 

Although the MTBE concentrations were low, the relatively 

high rate of detection illustrates how susceptible some aquifers 

are to low-level contamination and how quickly widespread 

groundwater contamination can occur from a widely used 

chemical. 

In 1999, a Blue Ribbon Panel on oxygenates in gasoline 

created by the EPA recommended that the requirement for 

an oxygenate in gasoline in large cities be dropped and that 

overall use of MTBE in gasoline be “reduced substantially” 

(U.S. Environmental Protection Agency, 1999). That same 

year, California ordered oil companies to phase out MTBE in 

gasoline by 2002 (later extended to 2003). By 2004, 19 States 

had enacted legislation to completely or partially ban MTBE 

use in gasoline (U.S. Environmental Protection Agency, 2004). 

The Energy Policy Act of 2005 eliminated the oxygen requirement in gasoline nationwide and accelerated the use of ethanol 

as an alternative. The use of MTBE and the subsequent rise in 

the use of ethanol indicate how air pollution, water pollution, 

and energy can be tightly linked with complex and sometimes 

unanticipated tradeoffs.

Figure F–1. Locations where methyl tertiary butyl ether (MTBE)

was detected in groundwater in the United States, 1985–2001. 

Most detections of MTBE in groundwater were in the highly 

populated New England and Mid-Atlantic States where MTBE use 

was high. (From Zogorski and others, 2006)

and gas wells be sealed after production ceases. Sealing 

typically involves setting plugs and (or) cementing portions of the well, particularly within and above the producing formation and within and below shallow freshwater 

aquifers (National Petroleum Council, 2011). However, 

poor industry guidelines, less-than-ideal materials, and 

weak or absent laws regarding well abandonment prior to 

1950 have left many areas of historic oil and gas production 

with an abundance of improperly sealed wells (National 

Petroleum Council, 2011). In some cases, well casings were 

completely removed for reuse, leaving the original wellbore 

open (Hammack and others, 2006). Improperly plugged 

and abandoned wells present an avoidable and potentially 

concerning avenue for the migration of brines, hydrocarbons, and surface contaminants to shallow aquifers (Shedlock, 1980; Osborn and others, 2011). In efforts to protect 

drinking water supplies, many States and energy companies 

have taken steps to locate and properly seal abandoned 

oil and gas wells, although this is a massive undertaking 

(Ground Water Protection Council, 2011). West Virginia 

alone has more than 12,000 known abandoned oil and 

gas wells (West Virginia Department of Environmental 

Protection, 2010). 

Transportation, storage, and processing of oil, natural 

gas, and produced waters can also affect water quality. It 

is estimated that more than 4 million kilometers (km) of 

pipelines for hazardous chemicals (mostly oil and gas) 

exist within the United States (U.S. Pipeline and Hazardous Materials Safety Administration, 2014b). In addition, 

there are more than 500,000 oil and gasoline storage tanks 

(U.S. Environmental Protection Agency, 2012b). Any of 

these pipes and tanks has the potential to develop leaks, 

and any leak has the potential to contaminate both surface 

water and groundwater. For the period 1994–2013, the 

U.S. Pipeline and Hazardous Materials Safety Administration (2014b) reported a total of 5,622 significant pipeline 

incidents; the resulting property damage was in excess of 

6 billion dollars. For 2011, more than 6,000 leaks from 

underground storage tanks were reported (U.S. Environmental Protection Agency, 2012b). Leaks can occur as the 

result of faulty materials, improper installation, and natural 

disasters such as hurricanes, earthquakes, and tsunamis, 

which can cause severe damage to energy infrastructure. As 

an example, more than 26 million L of oil reportedly leaked 

from pipelines and storage tanks around New Orleans in 

2005 as a result of Hurricane Katrina (Llanos, 2005).

Oil refineries are large industrial complexes that 

process millions of liters of crude oil daily. Operations conducted at these complexes release a variety of pollutants to 

the atmosphere—including carbon dioxide, volatile organic 

compounds, benzene, sulfur dioxide, and nitrous oxide—

that can contaminate water (U.S. Environmental Protection 

Agency, variously dated). Refineries can contain hundreds 

of storage tanks and reaction vessels as well as many 
Time

Volume produced

Oil

Water

Gas

EXPLANATION

A B

C D

22 The Water-Energy Nexus—An Earth Science Perspective

kilometers of pipelines. The extensive infrastructure and the 

high volume of material processing raise the potential for leaks 

that could eventually contaminate water. A leak at a refinery in 

Commerce City, Colo., which might have gone undetected for 

years, resulted in benzene contamination of shallow groundwater and the South Platte River (Finley, 2012). As mentioned 

above, catastrophic events such as Hurricane Katrina can also 

lead to contaminant releases in refineries. 

Produced Water

Natural gas and oil extracted from geologic reservoirs 

are usually intermixed with large volumes of produced water. 

Produced waters are a mixture of water naturally present in 

the reservoir, liquids used in the drilling and development 

process, and possibly hydrocarbon compounds associated with 

natural gas or oil. The chemistry of these waters vary, but they 

can be many times more saline than seawater and can include 

inorganic salts, dispersed oil, dissolved organic compounds, 

radionuclides, bacteria, and solids (Veil and others, 2004). 

Approximately 3.3 trillion L of produced water were 

generated in the United States in 2007 from about 1 million 

production wells (Clark and Veil, 2009). Currently, there is no 

national repository for quantitative information on produced 

water, but many states maintain databases containing the 

amounts of produced waters that are generated and the disposition or use of those waters. Clark and Veil (2009) compiled a 

table of produced water quantity and disposition on a state-bystate basis for 2007. Approximately 98 percent of produced 

water generated onshore in the United States in 2007 was 

injected into the subsurface (Clark and Veil, 2009); approximately 59 percent was injected into oil-producing formations 

as a part of secondary recovery operations to force oil toward 

producing wells, and almost 40 percent was injected solely 

for the purpose of disposing of the water. Only a small portion 

of produced waters in the United States presently is used for 

beneficial purposes, but recent research has led to increased 

efforts to identify beneficial uses of these fluids (see Box G—

Produced Waters—An Underused Resource?). Transport and 

treatment of large volumes of produced water continues to be 

an important management issue in the United States. 

Production rates for oil, natural gas, and water from 

individual wells vary depending on the specific resource being 

extracted, the type of reservoir, and the elapsed production 

time (fig. 7). Conventional oil and natural gas wells typically 

exhibit fairly rapid drop-off in hydrocarbon and water production. Shale-gas wells produce the majority of their water 

in the first few days of production, whereas oil wells tend to 

exhibit higher water-to-oil ratios as they mature (Clark and 

Veil, 2009). Veil and others (2004) noted, for instance, that the 

average water-to-oil ratio for operational wells in the United 

States increased from 7.5 to 9.5 L-water/L-oil between surveys 

conducted in 1996 and 2002; they attributed the increase in 

water production from increasingly mature fields. Obviously 

water flooding, as a form of secondary oil recovery, has potential to greatly increase the volume of water produced from a 

reservoir. In very late stage production, the water-to-oil ratio 

can be as high as 10–20 L-water/L-oil (Veil and others, 2004). 

In contrast, large volumes of water must be pumped from the 

coalbed natural gas reservoirs before gas can be extracted 

(fig. 7). Managing both water and hydrocarbon production can 

be complicated, especially across entire plays, where wells of 

differing maturity are operating at the same time.

Figure 7. Relative production 

of water and hydrocarbons 

from (A) a conventional oil well,

(B) a shallow conventional gas 

well, (C) a coalbed natural gas 

well, and (D) a shale gas well. 
Water in Energy Production and Use 23

Produced Waters—An Underused Resource?

Produced waters that are not injected back into 

the subsurface can be recycled and put to a variety 

of beneficial uses. Recycling of produced waters has 

two main benefits—reducing freshwater consumption and 

decreasing the volume of produced fluids to be disposed. 

Coalbed natural gas produced waters with relatively low 

salinity (less than 3,000 mg/L dissolved solids) in the Powder River Basin of Wyoming and Montana are being used 

for livestock and, after treatment, for irrigation of forage 

crops (Bern and others, 2013a,b). In cold regions, produced 

waters with high salinity (about 100,000 mg/L dissolved 

solids) are sometimes applied to roads to inhibit ice formation. Other industrial uses include dust control, equipment 

washing, input for steam conversion, and fire control (Veil 

and others, 2004).

In addition to reuse of produced waters, constituents 

within the waters might have economic value. Brines 

historically have been an important commodity in many 

Alfalfa field irrigated with pH-adjusted water from nearby coalbed 

natural gas wells, Johnson County, Wyoming.

Pilot-scale constructed wetland water-treatment system designed 

to break down and remove potential environmental contaminants 

in produced waters through biogeochemical processes.

parts of the United States. A variety of salts, calcium, 

magnesium, iron, bromide, and iodide can be produced for 

profit from brines after heating them in furnaces or evaporators (Price and others, 1937). Secondary chemicals such 

as hydrochloric acid can be produced from the bitterns of 

these fluids. More recently strategic commodities, such as 

lithium, an important element in the production of batteries, 

are being extracted from some produced waters (Engle and 

others, 2014).

Treatment of produced water might be required prior 

to use, discharge, or reinjection. Treatment technologies 

range from complete desalinization or distillation systems, 

which produces potable water, to passive constructed 

wetland systems that remove potential pollutants, such as 

oil and grease, salts, dissolved organics, suspended solids, 

metals, and radionuclides (Engle and others, 2014). Energy 

producers must weigh the economic tradeoffs involved in 

treatment, injection, and possible beneficial uses.

Coal

Coal continues to be the primary fuel for generation 

of electricity in the United States. In 2013, approximately 

890 million metric tons of coal were extracted in the United 

States, 91 percent of which was used to generate electricity (U.S. Energy Information Administration, 2014b). Water 

is associated with all stages of energy production from 

coal—extraction, transportation, processing, combustion, and 

disposal of waste products—bringing up issues of water supply and water quality. The importance of these issues depends 

on many factors, including mining method, climate, and the 

chemistry of the coal and adjacent rocks. 

Coal, which is found in many regions in the United States 

(fig. 8), is classified on the basis of rank, a measure of progressive alteration from lignite (low rank) to anthracite (high 

rank). Higher rank coals usually have greater energy contents. 

Coals in the eastern part of the United States generally have a 

higher rank than coals in the west. Western region coals, however, have lower sulfur contents per unit energy content and, 

hence, produce less sulfur-dioxide air pollution upon combustion. As a result, production from coal mines west of the 

Mississippi River increased substantially from 1970 to 2011 

(40.7 million to 579 million metric tons), whereas production from mines east of the Mississippi River remained fairly 
0 250 500 MILES

0 250 500 KILOMETERS

0 500 MILES

0 500 KILOMETERS

EXPLANATION

Anthracite (hardest)

Low-volatile bituminous coal

Subbituminous coal

Medium- and high-volatile 

bituminous coal

Lignite (softest)

Coal rank

Data from Schweinfurth and Finkelman, 2004

24 The Water-Energy Nexus—An Earth Science Perspective

steady at about 450 million metric tons per year for the same 

time period (U.S. Energy Information Administration, 2012a). 

Coal is extracted from both surface and underground 

mines. In surface mining, the rocks overlying the coal seam 

(the overburden) are moved to a temporary storage area, and 

the coal is extracted. The overburden might then be replaced, 

the land surface is recontoured to its approximate original 

position, and vegetation is replanted. Mountaintop removal 

mining is a large-scale form of surface mining that is commonly used in portions of the central Appalachian Basin, 

including Virginia, West Virginia, Tennessee, and Kentucky 

(U.S. Environmental Protection Agency, 2014e). In this process, entire mountaintops and ridges are removed to expose 

the underlying coal. As much as 300 meters (m) of overburden 

is removed, and much of it is deposited into adjoining valleys. Mountaintop removal mining can substantially alter the 

hydrology of a watershed—ditches are usually constructed to 

funnel runoff and drainage from the mine to a sedimentation 

pond and eventually to a flowing stream, natural stream channels and springs might be buried beneath overburden, and 

groundwater flow patterns can be disrupted. Post-mining reclamation efforts include recontouring of the land surface, but 

landscapes, hydrology, and ecosystems remain permanently 

altered (U.S. Environmental Protection Agency, 2014e).

Underground mines leave the overburden in place; the 

coal is extracted and transported to the land surface through a 

series of tunnels. Reclamation of underground mines usually 

includes returning the land surface to near pre-mining conditions and installing safeguards to minimize water drainage 

and subsidence from the network of tunnels (Gleick, 1994). 

Annual production from underground mines has remained 

fairly stable since 1950 at about 300 million metric tons 

(U.S. Energy Information Administration, 2012a), whereas 

production from surface mines increased steadily from 1950 to 

2011 (126 million to 679 million metric tons). 

Mountaintop coal removal mine in West Virginia 

during the reclamation process. The hills in 

the background are likely similar to the original 

topography and vegetation at the mine site.

Figure 8. Coal fields of 

the United States classified 

by rank. For each category 

of coal rank, the darker 

color indicates the area 

of coal outcroppings and 

the lighter color indicates 

the area of subsurface 

coal. (Modified from 

Schweinfurth, 2003)
Water in Energy Production and Use 25

A 439-km-long pipeline was used to transport coal from 

the Black Mesa mine in northern Arizona to the Mojave 

power plant in Nevada. It was the longest slurry pipeline 

in the world. Over the course of its operational life, from 

1969 to 2005, approximately 5.6 billion L of water were 

used annually to transport about 4.5 million metric tons of 

coal. The pipeline was controversial because the water 

was obtained from the Navajo aquifer. That aquifer is 

the major source of water for municipal and industrial 

uses for an area of about 14,000 km2 that has an arid to 

semiarid climate (Macy and others, 2012).

Water Use

Water is involved in all aspects of mining and processing of coal. For mining, the relevant issues are associated with 

mine dewatering, cooling of drilling equipment, cleaning of 

coal, dust suppression, waste disposal, reclamation, revegetation, and possibly transportation. Coal can be processed into 

gaseous or liquid fuels, operations which also require water.

Groundwater extracted for mine dewatering may or may 

not be viewed as consumed water. The extracted water can 

be used to satisfy many of the water needs of the mine, and 

excess water is usually discharged to a stream or other surfacewater body, keeping it in the hydrosphere. Mine dewatering, 

however, does affect natural patterns of groundwater flow; the 

diversion of groundwater to a mine may also affect nearby 

stream flows and associated ecosystems by reducing natural 

rates of groundwater discharge to land surface.

Rates of water withdrawal and consumption by coal 

mines are not routinely measured in the United States, and 

relatively few studies have attempted to estimate these 

rates. Lovelace (2009) suggests a water withdrawal rate of 

209–246 L per metric ton of coal, equivalent to a range of 

186–219 billion L of water withdrawn for all of the coal 

produced in the United States in 2013, or roughly 3 percent of 

all water withdrawn for mining in 2010 (Maupin and others, 

2014). Estimates of coal mine–related water consumption rates 

are provided in Gleick (1994), Pate and others (2007), Nicot 

and others (2011), and Meldrum and others (2013). Results of 

these studies suggest a wide range in water consumption rates 

for all phases of mining operations—between 75 and 500 L of 

water per metric ton of coal. The variability in these estimates 

is related to characteristics of the coal, mining processes, and 

methods used to generate the estimates. In general, the mining 

operation that consumes the most water is the irrigation of 

vegetation planted during reclamation—Grubert and Kitasei 

(2010) suggest 0.22 m of water per unit land surface area per 

year for a period of 10 years. 

Mine-related water storage can also affect human health 

and safety. On February 26, 1972, a dam constructed with 

coal-mine waste on a tributary to Buffalo Creek in southwestern West Virginia collapsed, sending 500,000 m3

 of water and 

mine waste down to the valley floor. The accident resulted in 

the loss of 125 lives and more than 500 homes in the town of 

Saunders (Davies and others, 1972).

Coal gasification is the chemical process of turning coal 

into natural gas that has been in use for more than 100 years. 

In the late 1800s, coal gasification was used to provide gas for 

home lights before the widespread availability of electricity. 

The Great Plains Synfuels Plant near Beulah, N. Dak., is currently the only commercial-scale coal gasification plant in the 

United States. On a daily basis, approximately 4.1 million m3

of synthetic natural gas is extracted from about 16,300 metric 

tons of lignite coal (Dakota Gasification Company, 2012). 

Water consumption rates for coal gasification, estimated to be 

in the range of 1.5–3.6 L/m3

 of gas (Gleick, 1994), are comparable to those for production of shale gas (table 1).

Continued on page 28
26 The Water-Energy Nexus—An Earth Science Perspective

Subsurface Fluid Injection—Risks of Groundwater Contamination and 

Earthquakes

Subsurface fluid injection refers to the process 

whereby fluids (most commonly water but also possibly wastes and carbon dioxide) are transferred from land 

surface to some depth in the subsurface through an injection well. The process has been in use in the United States 

for more than 100 years (Hickey and Vecchioli, 1986). 

Injection is used for a variety of purposes, such as the disposal of wastewater from municipal and individual (septic 

tanks) sources, aquifer replenishment, storm water disposal 

or storage, combatting salt water intrusion, and a number 

of energy-related purposes. Table H–1 and figure H–1 

describe the different classes of injection wells used in the 

United States. 

Subsurface injection was first used for disposal of 

produced waters from oil wells in the 1930s. Injection is 

still used for this purpose, but over the decades the number 

of energy-related applications of injection have expanded. 

Water is injected for secondary oil recovery, and CO2

commonly is injected for enhanced oil recovery; in these 

operations, the injected fluids are used to force residual oil 

to pumping wells. Solution mining for uranium relies on 

the injection of water and chemicals to extract the metal. 

Geothermal power plant managers use fluid injection to 

maintain pressures in geothermal reservoirs. Deep injection 

of CO2 is a key component of planned carbon capture and 

geologic sequestration programs.

Subsurface injection occurs throughout the United 

States. In the case of extraction of oil or minerals, the injection takes place in the location of the targeted asset. In the 

case of injection of produced water or wastewater, economics 

dictate that the injection point be located in proximity to the 

where the injectate is produced in order to minimize transportation costs; however, locating a suitable receiving formation 

can be problematic. Injection in oil fields can occur in production wells that have gone dry or in wells installed specifically 

for injection. Injection of CO2

 for future carbon sequestration will likely occur in the vicinity of a CO2

 source and will 

require installation of wells specifically for injection (see 

Box K—Carbon Capture and Sequestration). 

Host formations that receive injected fluids generally lie 

at depths of several hundred meters or more, much deeper than 

most aquifers that are used for drinking water. Primary storage space in these formations is created by displacing native, 

saline water. Smaller amounts of storage are created through 

the enhancement of total pore space in the native rock and by 

compression of the injected fluids. Potential adverse effects of 

subsurface injection include groundwater contamination and 

induced seismic activity. Groundwater can become contaminated if the injected fluid or displaced native water seeps into 

freshwater aquifers. Contamination can occur if the injection 

formation is not isolated from these aquifers; if the injection 

pressure is too high, causing inadvertent fracturing to occur; or 

if there are other avenues for water movement, such as abandoned wells or improperly completed wells. 

Induced seismicity refers to seismic activity (earthquakes) 

propagated by human actions. A number of activities, including the impoundment of reservoirs above dams, underground 

nuclear testing, and mining, are known to induce seismic 

Table H–1. Class, use, and number of wells in the U.S. Environmental Protection Agency Underground Injection Control Program in 

the United States in 2011.

[From U.S. Environmental Protection Agency (2012c). USDW, underground source of drinking water (aquifer with concentrations of total dissolved solids 

less than 10,000 milligrams per liter)]

Class Use 2011 Inventory

I Inject hazardous wastes, industrial nonhazardous liquids, or municipal wastewater 

beneath the lowermost USDW.

680 wells.

II Inject (1) brines and other fluids associated with oil and gas production, and 

(2) hydrocarbons for storage.

172, 068 wells.

III Inject fluids associated with solution mining of minerals beneath the lowermost 

USDW.

22,131 wells.

IV Inject hazardous or radioactive wastes into or above USDWs. These wells are banned 

unless authorized under a Federal or State groundwater remediation project.

33 sites.

V All injection wells not included in Classes I–IV. In general, Class V wells inject 

nonhazardous fluids into or above USDWs and are typically shallow, onsite disposal 

systems. However, there are some deep Class V wells that inject below USDWs.

400,000 to 650,000 wells. Note: 

an inventory range is presented 

because a complete inventory is not 

available.

VI Inject carbon dioxide (CO2

) for long-term storage, also known as geologic sequestration of CO2

.

6–10 commercial wells expected to 

come online by 2016.
Water in Energy Production and Use 27

Table H–2. Summary information on reported “felt” seismic 

events that could be attributed to energy-related activities.

[From National Research Council (2012). ~, aproximately; na, not applicable]

Technology Number of 

projects

Number of 

“felt” induced 

events

Maximum 

magnitude 

of induced 

events

Vapor-dominated 

geothermal 

systems

1 300–400/year 

since 2005

4.6

Liquid dominated 

geothermal 

systems

23 10–40/year 4.1

Enhanced geothermal systems~8 pilot studies 2–10/year 2.6

Oil field water 

flooding

~108,000 wells One or more 

events at 

18 sites

4.9

Enhanced oil 

recovery (EOR)

~13,000 0 na

Hydraulic fracturing—shale gas 

wells

~35,000 1 2.8

Hydrocarbon 

withdrawal

~6,000 fields 20 sites 6.5

Wastewater 

injection

~30,000 8 4.8

activity. The injection or withdrawal of fluids to or from a subsurface hydrocarbon or water reservoir can also trigger seismic 

activity; in most cases this is caused by a change in pore fluid 

pressure or stress in subsurface rocks near faults that have 

specific properties (National Research Council, 2012). The 

National Research Council examined the occurrence of seismic activity in the United States related to geothermal energy 

development, conventional oil and gas development, hydraulic 

fracturing of shale gas wells, and carbon capture and sequestration (National Research Council, 2012). They found that 

seismic events have been produced by these activities in the 

United States but that the number of events large enough to be 

felt was quite low relative to the number of injection and withdrawal wells in operation (table H–2). Most events occurred as 

a result of an imbalance in fluid pressures within a reservoir; 

balancing fluid pressures by a combination of injection and 

withdrawal appears to reduce the likelihood of seismic events. 

Only one seismic activity resulting from hydraulic fracturing 

of a shale gas well has been reported, and that incident has not 

been confirmed (National Research Council, 2012). In regard 

to carbon capture and sequestration, it is difficult to assess the 

likelihood of induced seismic activity arising from CO2

injection because there were no commercial-scale operations in the United States as of 2013; however, injection of 

CO2 for sequestration could pose a greater risk of inducing 

seismic activity than other energy technologies because 

of the large volumes of CO2 that are involved (National 

Research Council, 2012). 

In order to promote successful subsurface fluid 

injection, Hickey and Vecchioli (1986) suggested that 

the injection site and surrounding area satisfy a number 

of hydrogeologic criteria, including (1) that the injection 

zone should be regionally extensive, not be penetrated by 

improperly abandoned wells, and be overlain and underlain 

by confining beds that will retard movement of injected 

fluids; (2) that the injected fluid be chemically compatible 

with the native rock and groundwater so as to avoid reactions that could plug the injection zone or produce toxic 

substances; and (3) that mineral or hydrocarbon resources 

be absent from the injection zone to preclude the possibility 

of future development.

Figure H–1. Class I, II, and III wells, left to right, as defined 

by the U.S. Environmental Protection Agency Underground 

Injection Control Program. (From U.S. Environmental Protection 

Agency, 2012c)
28 The Water-Energy Nexus—An Earth Science Perspective

Coal liquefaction is a two-step process for turning coal 

into liquid fuels, such as gasoline, diesel, and kerosene, primarily for use in motor vehicles (National Energy Technology 

Laboratory, 2006). The first step consists of coal gasification. 

The second step converts the gas to liquid form by the addition 

of water and carbon dioxide. Coal liquefaction technology 

is well known, and the fuel that is generated can serve as a 

substitute for fuels derived from crude oil. Some countries 

with limited crude oil resources, such as South Africa, rely 

on coal to produce a large percentage of their transportation 

fuels (World Coal Association, 2014). Currently (2014), no 

domestic commercial coal liquefaction plants are in operation 

in the United States. Water consumption rates for production 

of fuel by coal liquefaction have been estimated at 5–7.3 L of 

water per liter of fuel (National Energy Technology Laboratory, 2006). 

Water Quality

Water-quality concerns are often as important as those of 

water supply in regard to coal mining. Nationally, acid mine 

drainage is perhaps the most significant water-quality issue 

associated with coal extraction. Coal and rocks adjacent to 

coalbeds often contain sulfide minerals such as pyrite. When 

these rocks are exposed to air and water, oxidation reactions 

release sulfur and allow the formation of sulfuric acid. The 

resulting decreased pH levels in groundwater and surface 

water lead to increased concentrations of heavy metals, which 

may in turn render the waters toxic to fish and other aquatic 

life (Nordstrom and Alpers, 1999). 

Acid mine drainage (AMD) can occur as a result of direct 

discharge of water used in coal-mining operations, such as 

for coal washing and dust suppression. It can also be generated when precipitation infiltrates coal and rock-waste piles 

at surface mines or when spoil retention dams fail. If underground mine shafts or surface waste piles are not properly 

sealed, AMD can occur for decades after a mine has been 

closed. Coal mines may be the largest source of AMD in the 

United States, but other mines, such as for gold, copper, and 

uranium, also produce AMD. A quantitative assessment of 

water contamination from AMD has not been conducted at the 

national level, but regional and local patterns are evident. A 

greater abundance of water and a higher sulfur content of coal 

make the eastern half of the United States more susceptible 

to AMD than the western half of the country. For example, 

AMD has affected approximately 2,100 km of streams in Ohio 

(Ohio Department of Natural Resources, 2014) and more than 

4,300 km of streams in West Virginia (Corio, 2008).

Interestingly, mountaintop removal mining has been 

shown to reduce acid-mine drainage; water from these mines 

can be neutralized by minerals in the valley fill (Griffith and 

others, 2012). Constructed sedimentation ponds also facilitate 

water treatment to raise pH and reduce concentrations of metals. Nevertheless, mountaintop removal mining alters natural 

ecosystems, and streams draining valley fills tend to have 

higher concentrations of dissolved solids relative to unaffected 

streams (Lindberg and others, 2011; Griffith and others, 2012).

Uranium

Fuel for nuclear power plants comes from traditional 

surface and underground uranium mining and, more recently, 

from in-place extraction or leach mining. Production of 

nuclear fuel rods requires several levels of uranium processing 

(Gleick, 1994). Uranium ore extracted by traditional mining 

is chemically separated from other materials at a uranium 

mill and converted to yellowcake (U3O8). In-place extraction 

yields yellowcake directly. The yellowcake is then converted 

to uranium hexafluoride (UF6) or uranium dioxide (UO2). At 

this point, uranium is enriched. Naturally occurring uranium 

contains about 0.72 percent uranium-235 (the remainder is 

uranium-238, which is non-fissile). To increase energy content, the relative amount of uranium-235 must be increased to 

Former site of the small town of Saunders, West Virginia, in 

the aftermath of the Buffalo Creek flood of February 26, 1972.

Acid mine drainage in an open limestone channel near Huntsville, 

Missouri.
Injection well

Potentiometric surface of

 lower aquifer (exaggerated)

Less permeable strata

Perforations

Less permeable strata

Ore-bearing sand

Perforations

Upper

aquifer

Lower

aquifer

Water in Energy Production and Use 29

3–4 percent. Enrichment has historically been done by a gasdiffusion process; most newer enrichment facilities use gas 

centrifuges arranged in cascading series. The final processing 

step is fabrication of the fuel rods from the enriched uranium.

Uranium mining in the United States began in earnest in 

the 1940s. Annual production has varied substantially over the 

years, mostly in response to economics. Annual production 

in 2013 was about 2,080 metric tons of U3

O8, a substantial 

decrease from the highpoint of 1980, when 16,810 metric tons 

were produced. Since the 1990s, most of the uranium used in 

the United States is imported from other countries. A total of 

10 uranium mines were operating in the United States in 2013. 

Seven of these mines used in-place leaching; the other three 

active mines were traditional underground mines (U.S. Energy 

Information Administration, 2014c). Only one uranium mill, 

for processing ore from traditional mines, was operational in 

the United States in 2013.

Water Use

Water is used in all steps of uranium extraction and 

processing. Similar to coal mining, traditional uranium 

mining at underground or surface mines requires water for 

dust control, equipment washing, remediation, and revegetation. In-place leach mining (fig. 9) has different water needs. 

In-place leach mining uses a series of injection and extraction wells: water and chemicals are injected into an aquifer, 

the mixture dissolves the uranium, and the groundwater is 

pumped to the surface, where the uranium is removed. The 

process is repeated until uranium can no longer be economically recovered. Estimates of water consumption for mining 

and milling from traditional surface and underground mines in 

Australia, Africa, and North America ranged from about 400 

to 800 L-water/kg of yellowcake in 2005 (Mudd and Diesendorf, 2008). This same study found that a single in-place 

leach mine required about 8,800 L-water/kg of yellowcake. 

The higher water consumption with in-place leach mining is 

largely related to production and subsequent evaporation of 

waste sludge and wastewater. Mudd and Diesendorf (2008) 

also noted that lower grade ore deposits require more water for 

processing. Conversion of yellowcake to UF6

 or UO2 (depending on the type of reactor) consumes about 10,000 L-water/kg 

of 3.5-percent enriched uranium, whereas enrichment by gas 

centrifuges consumes about 5,100 L-water/kg of enriched 

uranium (Gleick, 1994). The final step in fuel processing, fabrication of fuel rods, consumes an estimated 2,500 L-water/kg 

of enriched uranium (Gleick, 1994). 

Spent fuel and other radioactive by-products can be 

re-processed for reuse, thereby garnering additional thermal 

heat, but large quantities of water are required for this process—estimates are as high as 130,000 L-water/kg of enriched 

uranium (Gleick, 1994). Commercial reprocessing is not currently being done in the United States, but it is done in several 

countries, including France, the United Kingdom, Russia, and, 

more recently, China.

Figure 9. In-place recovery 

of uranium using chemical 

leaching compounds. Dashed, 

arrow-tipped lines show 

hypothetical flow paths of 

injected leaching solutions 

in the subsurface. (From 

U.S. Nuclear Regulatory 

Commission, 1997)
0

10

20

30

40

50

60

1980 1990 2000 2010 2020

Production, in billions of liters

Year

Bioethanol

Biodiesel

EXPLANATION

30 The Water-Energy Nexus—An Earth Science Perspective

Water Quality

Potential contamination of water resources from extraction and processing of uranium continues to be an issue of 

concern, primarily at mining and milling sites. Although only a 

small number of domestic mines and mills are currently active, 

uranium-related activities since the 1940s have left a legacy of 

abandoned mines and mills across some western States. Many 

of these sites continue to contaminate air and water resources. 

It is estimated that there are 4,000 uranium mines in the states 

of Wyoming, New Mexico, Utah, Colorado, and Arizona that 

are no longer in production. These mines, as well as many 

abandoned mills, are current or potential sources of water contamination. Acid-mine drainage, similar to that described for 

coal mining, and contamination of water supplies by uranium, 

radium, and other radionuclides are the most important concerns from a water resources perspective (U.S. Environmental 

Protection Agency, 2013a). Although in-place leach mining 

causes little surface disturbance and leaves no tailings, it still 

generates waste products. If not properly managed, in-place 

mining can lead to groundwater contamination. 

Biomass

The term “biomass” refers to renewable fuels that are 

produced from plants and animals. This category can be 

broken down according to fuel use: those used for transportation and those used to generate electricity and heat. Transportation fuels are referred to as “biofuels,” and fuels used 

for electricity and heat are “wood and waste.” The two most 

common biofuels are bioethanol and biodiesel. These fuels are 

used as replacements for or additives to gasoline and diesel 

fuel. “Wood and waste” refer to wood and biogenic wastes 

or byproducts from agricultural, industrial, and municipal 

processing. Wood is the most prominent biomass fuel; it has 

traditionally been used to heat homes and other buildings and 

is still used for this purpose. In 2013, it accounted for about 

23 percent of all renewable energy used in the United States, 

more than bioethanol and biodiesel combined (U.S. Energy 

Information Administration, 2014b). About 30 percent of 

wood consumption in that year was for home and commercial 

heating and about 70 percent was for generating electricity 

and providing heat for industry. Because wood is not grown 

commercially as a fuel, irrigation is not a source of water consumption. Small amounts of water may be required for processing of raw wood (such as for making wood pellets) prior 

to being consumed, but these amounts are generally inconsequential. As such, the remainder of this section addresses 

production and processing of biofuels.

Production of biofuels has increased steadily over the 

past decade, both within the United States (fig. 10) and worldwide. In 2013, about 55 billion L of biofuel were produced 

within the United States, about 5 percent of all domestic 

transportation fuels (U.S. Energy Information Administration, 

2014b). A number of factors have played into the heightened 

interest in biofuels—national security (the desire to reduce the 

Nation’s energy dependence on other countries), a desire for 

lower energy costs, and a desire to reduce the carbon footprint of traditional hydrocarbon transportation fuels. Biofuel 

production within the United States is largely driven by the 

U.S. Energy Independence and Security Act of 2007 (EISA), 

which called for 34 billion L of renewable fuels by the year 

2008 (38 billion L were actually produced) and 136 billion L 

by the year 2022. Europeans have set similar goals, with 

renewable fuels required to account for 10 percent of all 

transportation fuels by the year 2020 (European Union Commission, 2009). Brazil, the second largest producer of biofuels 

behind the United States, requires that all gasoline be blended 

with ethanol at ratios of 3:1 (E25) to 4:1 (E20) (U.S. Energy 

Information Administration, 2013a). 

Uranium mine and tailings, Emery County, Utah.

Figure 10. Annual production of biofuels in the United States, 

1981–2013. (Data from U.S. Energy Information Administration, 

2014b)
Year

20

25

30

35

40

45

2000 2005 2010 2015

Planted corn, in millions of hectares

Water in Energy Production and Use 31

Water is required for growing the raw material (referred 

to as feedstock) used to produce biofuels and for converting 

the feedstock to fuel at refineries. Crop water requirements 

vary substantially depending on feedstock, climate, and soils. 

Many crops thrive on natural precipitation in humid and subhumid regions of the United States, whereas irrigation may be 

required in more arid regions. We only consider applied irrigation water in estimating water consumption rates for growing 

biofuels. In addition, agricultural chemicals such as fertilizers and pesticides are often applied to enhance production 

rates; these chemicals can potentially lead to contamination 

of surface water and groundwater (Gilliom and others, 2006; 

Dubrovsky and others, 2010).

Water Use for Bioethanol

Sugar and starch crops currently (2014) constitute 

the largest feedstocks for bioethanol production, with corn 

being the most popular fuel source in the United States and 

sugarcane in Brazil. On the basis of energy content and water 

requirements, it is widely accepted that corn is not the optimal 

fuel source for bioethanol production (U.S. Environmental 

Protection Agency, 2014d). Corn is currently being used in 

the United States because farmers have a great amount of 

experience growing corn and because techniques for converting grain to ethanol are well understood. The U.S. Congress, 

however, acknowledged the limitations for corn-based ethanol 

production; it mandated in the EISA that 58 percent of the 

136 billion L of biofuel produced in 2022 be derived from cellulosic material (such as perennial grasses and wood) or other 

non-corn feedstocks. The reasoning was two-fold: to promote 

the most efficient fuel sources and to avoid the competition for 

grain between food and energy interests. Corn and sugarcane 

are referred to as “first generation” feedstocks; water requirements for growing and processing these crops are well known 

because operations are currently active. Less understood are 

the water requirements for “second generation” cellulosic 

feedstocks such as the perennial grasses switchgrass (Panicum 

virgatum) and miscanthus because these crops have not been 

grown in large-scale farms and refining techniques are still 

under development.

Irrigation accounts for most water consumption in 

bioethanol production. Water requirements for corn depend 

on climate, soil, landscape, and growth stage of the plant, but 

corn typically requires 400–650 millimeters (mm) of water 

during the growing season (Wu and Chiu, 2011). Corn can 

be grown without irrigation in much of the eastern half of the 

United States where the climate is subhumid to humid, but 

irrigation is sometimes used in these regions if water is readily available. In the more arid western regions of the United 

States, it is difficult to grow corn without irrigation. 

Approximately 50 billion L of ethanol were produced in 

the United States in 2013 (U.S. Energy Information Administration, 2014b), consuming about 4.7 billion bushels of corn, 

roughly 34 percent of the total corn harvest of 13.9 billion 

bushels. The amount of land planted in corn has generally 

increased since the year 2000 (fig. 11), mirroring the price 

of corn. The increased acreage includes the addition of new 

crop land as well as the conversion of existing crop land from 

other crops to corn. The amount of irrigated corn acreage also 

increased between 2002 and 2007, though the percentage of 

corn acreage under irrigation remained relatively constant at 

about 12 percent (U.S. Department of Agriculture, 2010). The 

total amount of water withdrawn for corn irrigation increased 

only slightly from 14.4 trillion L in 2002 to 14.8 trillion L 

in 2007; more land was put under irrigation, but the actual 

amount of applied water increased only by about 2 percent. 

Water consumed in growing corn for ethanol can be estimated with the numbers provided in the previous paragraph by 

making a few simple assumptions. We assume that irrigation 

rates for 2013 were similar to those for 2007 (the most recent 

year for which data are available [U.S. Department of Agriculture, 2014]) and that 40 percent of the water withdrawn 

for corn irrigation can be allocated to ethanol production. 

Following the approach of Wu and others (2009) and Wu and 

Chiu (2011), we also assume that 71 percent of that water is 

consumed by the crop (the remaining 29 percent is returned 

to the biosphere) and that 67 percent of the consumed water 

is allocated to ethanol (the remaining 33 percent is allocated 

to co-products generated by refinery operations). Under these 

assumptions, the water consumption rate for growing corn 

for ethanol in 2013 is about 56 L of water per L of ethanol 

(L-water/L-ethanol), similar to the estimate of Wu and Chiu 

(2011) of 51 L-water/L-ethanol for three corn growing regions 

of the United States in 2008.

Figure 11. Annual hectares of planted corn in the United States, 

2000–2013. (From U.S. Department of Agriculture, National 

Agricultural Statistics Service, 2014)
32 The Water-Energy Nexus—An Earth Science Perspective

The conversion of corn and other grains to bioethanol at 

refineries also requires water. Most water used in the refinery 

is used for cooling, although water is also used for feedstock 

preparation and fermentation. Refineries have reduced the 

amount of water needed to produce ethanol since the early 

models of the late 1990s. Early refineries used as much as 

11 L-water/L-ethanol (Shapouri and Gallagher, 2005), whereas 

average withdrawal and consumption for 2008 were reported 

to be 2.7 L-water/L-ethanol and 2.3 L-water/L-ethanol, respectively (Mueller, 2010). These water-use numbers are small 

relative to those for irrigation, but refinery water requirements 

can be significant on a local level. As of November 2013, 

there were 210 bioethanol refineries in operation within the 

United States with a total bioethanol production capacity of 

56 billion L/yr (Renewable Fuels Association, 2013). The 

average bioethanol production capacity per plant is about 

266 million L/yr. At a water withdrawal rate of 2.7 L-water/Lethanol, about 720 million L of water per year are required on 

average for each plant. 

Attaining the EISA goal for production of 60 billion L 

of cellulosic bioethanol by the year 2022 faces significant 

challenges. The technology for large-scale conversion of cellulosic material to ethanol is still under development; there 

were no commercial refineries that could do the conversion 

operating in the United States in 2013. In addition, cellulosic 

feedstocks would soon need to be grown on a large scale. 

Perennial grasses such as switchgrass and miscanthus have 

been suggested as possible feedstocks—fields of miscanthus 

can produce about 10,000 L of ethanol per hectare without 

irrigation, yields almost 50 percent higher than those for corn 

(Extension, 2014). However, conversion of large amounts of 

farmland from a traditional corn/soybean rotation to perennial 

grasses may be difficult. To produce 60 billion L of ethanol 

Perennial grasses such as switchgrass and miscanthus have 

qualities that make them potentially well suited for use as feedstock. 

These grasses have a high resistance to pests and low fertilizer 

requirements, and they can tolerate droughts as well as floods. 

Different varieties of these grasses grow in all areas east of the Rocky 

Mountains (Extension, 2014).

with current technology, at least 6 million hectares of farmland will need to be planted in perennial grasses. Six million 

hectares represent about 15 percent of all land planted in 

corn in the United States in 2013. Farmers will face logistical 

as well as cultural difficulties adapting to such a large-scale 

change in farming practices. In light of these uncertainties, it 

is not possible to predict water requirements for production of 

cellulosic bioethanol.

Water Use for Biodiesel

Biodiesel is a fuel made from natural oils and greases 

that can be used as a replacement for traditional diesel fuel. In 

2013, approximately 5.1 billion L of biodiesel were produced 

in the United States (U.S. Energy Information Administration, 

2014b). Soybean oil accounted for about one half of the feedstock; the other half consisted of a mixture of other vegetable 

oils (such as canola, cottonseed, and palm) and animal fats. 

Production of biodiesel in the United States has followed a 

general upward trend since 2000 (fig. 10). In 2013, roughly 

10 percent of all soybeans grown in the United States were 

converted into biodiesel.

The amount of water consumed in developing biodiesel 

cannot be accurately determined because of the many different types of feedstock. As with bioethanol, the largest water 

requirement for biodiesel pertains to irrigation of the feedstock 

crops. In 2007, 2.8 million hectares of soybeans were irrigated 

in the United States with a total amount of 6 trillion L of water 

(U.S. Department of Agriculture, 2010). If we assume that biodiesel feedstocks have the same water and irrigation requirements as soybeans, then 10 percent of the water used for irrigation of soybeans can be allocated to biodiesel production. If 

we further assume, as with bioethanol, that irrigation rates for 

2013 were similar to those of 2007, that 71 percent of irrigation water is consumed by the crop, and that 67 percent of that 

irrigation is allocated to biodiesel (the remaining 33 percent is 

allocated to refinery byproducts), it follows that the production 

of 5.1 billion L of biodiesel in 2013 consumed about 290 billion L of water or about 57 L-water/L-biodiesel. Biodiesel 

refineries typically consume 1 to 3 L-water/L-biodiesel (Pate 

and others, 2007). 

Future trends in biodiesel production largely depend on 

development of new feedstocks. Research efforts are currently 

underway to improve techniques for producing oil from algae, 

with the hope of developing economically viable commercial 

operations. The potential rewards of developing this algae 

feedstock are substantial. Whereas a hectare of corn can 

produce up to 5,200 L of ethanol, and a hectare of soybeans 

can produce 840 L of biodiesel, a hectare devoted to algae has 

the potential to produce 9,400–59,000 L of biodiesel (Chisti, 

2008). In addition, algae can grow with water of marginal 

quality. Because no commercial algae/oil production plants are 

operational, however, water requirements are unknown.
Coal

(39 percent)

Natural gas

(27 percent)

Nuclear

(19 percent)

Other

(3 percent)

Hydroelectricity

(7 percent)

Wind and solar

(4 percent)

Water in Energy Production and Use 33

Water Quality and Biofuels

Growing crops for biofuel production raises some 

water-quality concerns. Corn requires substantial amounts of 

nitrogen to grow, as much as 0.45 kg per bushel of yield per 

year. Pesticides such as acetochlor, atrazine, and glyphosate 

are commonly used to control weeds in corn fields. Surface 

water and groundwater in much of the central United States 

have become contaminated with high levels of nitrates and 

pesticides (Gilliom and others, 2006; Dubrovsky and others, 

2010). Watersheds in the upper Midwest contribute substantial 

amounts of nitrogen to streams. Annual nitrogen loads for the 

reaches of the Iowa River for 2004 and 2008 were between 

400 and 6,800 kg per square kilometer of contributing drainage area (Garrett, 2012), and from 1985 through 2012, annual 

discharge of nitrogen to the Gulf of Mexico ranged from 0.7 

to more than 2.2 million metric tons (U.S. Geological Survey, 2013). The transition from corn to cellulosic feedstocks, 

however, may eventually lead to some reduction in nitrogen 

and pesticide contamination of the Nation’s water resources. 

Unlike corn, soybeans do not require application of nitrogen 

fertilizers (though they are commonly treated with pesticides 

and other fertilizers).

Water contamination from bioethanol and biodiesel refineries has not been widely reported. Indeed, there is usually 

little waste from these refineries. Byproducts such as distillers 

dried grain and solubles (DDGSs) are used for animal feed 

and other purposes, and other byproducts can be combusted 

and used to provide heat or to generate electricity to sustain 

refinery operations (Wu and Chiu, 2011). 

Electrical Power Generation

Generation of electricity accounts for about 40 percent 

of all energy consumption in the United States. Most forms 

of electricity generation also consume water, much more 

water, in general, than other energy development activities. 

The previous section discussed water requirements for different fuels, many of which are used to generate electricity. 

This section examines water withdrawal and consumption 

and water-quality issues associated with power plants that 

generate electricity. Water consumption is presented in terms 

of water intensity, in units of liters of water consumed per 

generated kilowatthour of electricity (L/kWh). A less waterintensive process consumes less water to generate a unit of 

electrical power. 

The availability of water is fundamental to most electricity generation. For example, hydroelectric power plants use 

the energy of falling water to drive turbine generators, and 

thermoelectric power plants require water for cooling and 

condensing the steam used to drive turbine generators. Water 

use for thermoelectric plants constitutes the single largest 

withdrawal of water in the United States; in 2010, thermoelectric power generation accounted for about 45 percent of 

all freshwater withdrawals (Maupin and others, 2014). Wind 

and solar photovoltaic power plants, on the other hand, are 

somewhat unique in that they generate electrical power with 

relatively small water requirements; these plants are growing 

in popularity but still constitute a small portion of the total 

electrical power capacity in the United States (fig. 12).

Thermoelectric Power Plants

Thermoelectric power plants generate about 89 percent 

of the electricity in the United States (U.S. Energy Information Administration, 2014b). As the name implies, these plants 

convert thermal energy to electrical energy, mostly through the 

use of steam turbines. Water is boiled within a closed system 

to create steam, and the steam drives the turbine generators that create electricity. After passing through the turbine 

generators, the steam is cooled and condensed back to liquid 

form, and the water is reused in the cycle. The cooling process 

accounts for more than 90 percent of all water withdrawal and 

consumption at most plants. Thermoelectric plants are fueled 

primarily by coal, natural gas, and nuclear energy (fig. 12). 

Other thermoelectric plants, powered by geothermal or solar 

energy, are important on a regional basis but account for less 

than 1 percent of generated electricity on the national scale. 

Water Use for Thermoelectric Plants

Water use in electricity generation is controlled primarily 

by three factors: 

• Energy content of fuel used in the process—Energy 

content refers to the energy released or available when 

a unit mass or volume of fuel is consumed. The concept is identical to the calorie content of foods we eat: 

calories are a measure of energy, and foods are fuel for 

the human body. Energy contents for selected fuels are 

shown in table 2.

• Type and thermal efficiency of the power plant—Thermal efficiency refers to the ratio of electrical energy 

produced in a power plant to the heat or thermal energy 

of the fuel that is consumed in the process.

• Type of cooling system that is used—Most cooling 

systems rely on water to dissipate heat, but air can also 

be used.

Figure 12. Total 

electricity generation 

in the United States 

by fuel, 2013. “Other” 

includes biomass, oil, 

waste incineration, 

and geothermal 

power. (Data from 

U.S. Energy Information 

Administration, 2014b)
34 The Water-Energy Nexus—An Earth Science Perspective

Table 2. Energy contents of selected fuels.

[kWhth, kilowatthours of thermal energy; kg, kilogram; m3, cubic meter; 

L, liter]

Fuel Energy content

Coal—bituminous 7–9.7 kWhth/kg

Coal—subbituminous 5.3–8.3 kWhth/kg

Coal—lignite 3.6–5.3 kWhth/kg

Natural gas 10.6 kWhth/m3

Wood 4.5 kWhth/kg

Fuel oil 10.6–11.8 kWhth/L

Uranium-235 2.3×107

 kWhth/kg

Gasoline 8.9 kWhth/L

Diesel 10 kWhth/L

Bioethanol 5.1–5.9 kWhth/L

Biodiesel 9.3–9.9 kWhth/L

Power Plant Thermal Efficiency

Thermal efficiencies of thermoelectric power plants 

vary with plant type and fuel (table 3). For example, coalfired steam-turbine plants typically have an efficiency of 

about 34 percent. In other words, about 34 percent of the 

energy stored in coal is converted into electrical energy; the 

remaining 66 percent of the thermal energy is used for plant 

operations, transferred to the cooling water, or lost through 

the smokestack. In addition to steam turbines, electricity can 

be generated by combustion turbines and combined cycle 

systems. Combustion turbines (sometimes referred to as gas 

turbines) are driven directly by the combustion of natural gas. 

They are typically run for short periods of time to meet peak 

demands for electricity and require no cooling water. They 

accounted for about 3 percent of electricity generation in the 

United States in 2012 (U.S. Energy Information Administration, 2013b). Thermal efficiency of combustion turbines, 

about 30 percent (Scanlon and others, 2013), is less than that 

Table 3. Power plant thermal efficiency and water consumption rates for different types of electricity generation in terms of 

water intensity (in liters of water per kilowatthour of generated electricity).

[L/kWh, liters of water per kilowatthour of electricity; na, not applicable; --, unknown]

Plant type Thermal efficiency 

(percent) Cooling process

Range of reported power plant 

water consumption rates 

(L/kWh)

Coal—steam turbine 1

34 Once-through 2,80.2–1.2

1

34 Tower 2,81.6–2.5

Nuclear—steam turbine 1

33 Once-through 30.4–1.5

1

33 Tower 32.2–3.4

Natural gas—steam turbine 1

33 Once-through 3,80.7–1.7

1

33 Tower 32.1–4.2

Natural gas—combined cycle 1

45 Once-through 30.1–0.9

1

45 Tower 30.2–1.1

Natural gas—combustion turbine 9

30 na na

Biomass 1024 Tower 2

1.8–3.6

Geothermal (binary) 4

8–16 Tower 56.8–9.9

Geothermal (flash) -- na 6

3.3

Concentrating solar power (parabolic trough) -- Tower 3

2.1–7.2

Hydroelectric -- na 7

3.5

1

U.S. Energy Information Administration (2012a).

2

Macknick and others (2012).

3

Meldrum and others (2013).

4

DiPippo (2007).

5

Mishra and others (2011).

6

Adee and Moore (2010).

7

Value for hydroelectric power is for reservoir evaporation from 

example in this report.

8

Diehl and Harris (2014).

9

Scanlon and others (2013).

10 Wiltsee (2000).
0

20

40

60

80

100

120

140

160

180

200

Jan.

Mar.

May

Sept.

Nov.

Mar.

May

Sept.

Nov.

Electricity generation, in billions of kilowatthours 

Coal

Natural gas

Nuclear

Renewables

July

Jan.

July

Month

Water in Energy Production and Use 35

for gas steam turbines. Combined-cycle natural gas power 

plants have two electricity-generating cycles: the first cycle 

uses a combustion turbine, and the second cycle captures the 

exhaust from the combustion turbine and uses it as the heat 

source for a steam-driven turbine. Combined-cycle natural gas 

power plants have an average thermal efficiency of 45 percent 

(table 3).

Other factors can affect power-plant thermal efficiency, 

including demand for electricity, air temperature, and ambient 

cooling water temperature. As a result, thermal efficiency varies with climate and location, as well as with season and time 

of day. Thermoelectric power plants are least efficient during 

summer months because warmer air and water temperatures 

make it difficult to cool the system. In addition, peak electrical demands often occur in summer months because of heavy 

air conditioner use (fig. 13). Increased electrical demand and 

decreased thermal efficiency mean that water consumption at 

any thermoelectric power plant is usually highest in summer 

months.

Thermal efficiency of power plants is linked to water 

intensity in complex fashions. For water-cooled systems, the 

amount of cooling water required varies with the amount of 

fuel consumed. If the amount of fuel consumed per kilowatthour of electricity is reduced, then less water is consumed. 

At the same time, more effective cooling can enhance 

thermal efficiency. 

Figure 13. Monthly net electricity generation in the United States 

by source, January 2011–December 2012 (U.S. Energy Information 

Administration, 2014b). Coal- and gas-generated electricity 

show distinct seasonal trends, with the highest rates of power 

generation in summer months and secondary highs in winter 

months. (Renewables include hydroelectricity, wind, biomass, 

solar, and geothermal.)

Power Plant Cooling Systems

The three general types of cooling systems are oncethrough (also known as open-loop), wet recirculating (also 

known as closed-loop), and dry. In once-through cooling systems water is withdrawn from a surface-water body, circulated 

through the system to absorb heat, and then discharged back 

into the surface-water body (fig. 14). The availability of large 

volumes of water is essential to the operation of once-through 

systems. These systems have relatively high rates of water 

withdrawals, but most of the withdrawn water is returned to 

the surface-water body, albeit at temperatures several degrees 

warmer than ambient conditions. Once-through systems 

have relatively low rates of onsite water consumption, but 

additional consumption of water occurs offsite. The warmer 

temperature of the discharged water promotes increased or 

“forced” evaporation downstream in the original water body 

(Diehl and others, 2013). Onsite water consumption can be 

monitored with meters, but there is no direct way to measure 

the amount of water consumed offsite as forced evaporation. 

See Diehl and others (2013) for a thermodynamics-based 

technique for estimating forced evaporation from power plant 

cooling systems. 

The Federal Water Pollution Control Act of 1972 and 

recent regulations issued by the U.S. Environmental Protection 

Agency (2014c) placed restrictions on the use of once-through 

cooling systems for new power plants because of concerns 

about environmental effects. As a result, most thermoelectric 

plants installed since the mid-1970s are equipped with a wet 

recirculating cooling system, a closed-loop system in which 

water is circulated through the cooling system to absorb heat, 

the water itself is then cooled, and that water is recirculated 

(fig. 14). These cooling systems have relatively low rates of 

water withdrawal, but most of the water withdrawn is consumed through evaporative loss, resulting in higher water 

consumption than once-through systems. Tower-based systems 

account for about 85 percent of the electricity produced with 

recirculating systems, and the remaining systems use cooling ponds (Diehl and Harris, 2014). Small ponds consume 

water at rates similar to tower systems, whereas large ponds 

resemble once-through systems in their water consumption. 

A fraction of the water being recycled through a recirculating 

system must be discharged to prevent salts from reaching concentrations that cause scaling problems. This water is called 

“blowdown.” The water that is withdrawn to replace evaporative losses and blowdown is known as “make-up water.” Wet 

recirculating cooling systems using cooling towers typically 

consume about 30 to 70 percent more water per kilowatthour 

of electricity produced than once-through cooling systems 

(table 3) (T.H. Diehl, U.S. Geological Survey, written commun. 2013). 

Dry cooling systems rely on heat exchange with ambient 

air, rather than water, for cooling; water withdrawal and consumption, therefore, are minimal for these systems. However, 

dry cooling is not as effective as wet cooling and can result in 
Turbine/generator

Boiler Condenser

Heat

High

pressure

steam

Low

pressure

steam

Liquid

water

Condenser

River

• Higher water withdrawal

• Lower water consumption

• Return flows affect water 

 temperature

A

B

Condenser

River

• Lower water 

 withdrawal

• Higher water 

 consumption

C

Blowdown

Tower

Make-up

water

36 The Water-Energy Nexus—An Earth Science Perspective

significant thermal efficiency and energy capacity penalties 

during hot weather conditions. To address these limitations, 

hybrid wet/dry systems are being researched and developed. 

Hybrid systems commonly involve separate dry and wet units 

installed in parallel. The wet system may operate only on the 

hottest days to evaporatively cool the air going to the aircooled condenser. In the United States, approximately 43 percent of thermoelectric generating capacity uses once-through 

cooling, 42 percent uses wet recirculating with cooling towers, 

14 percent uses wet recirculating with cooling ponds, and 

1 percent uses dry cooling (National Energy Technology 

Laboratory, 2011). 

Figure 14. Schematic and general characteristics of (A) a steam 

thermoelectric power plant with water cooling, (B) a once-through 

cooling system, and (C) wet recirculating systems with cooling 

towers. Boiler water is contained in a closed system and does not 

mix with cooling water. 

Water Withdrawal

Approximately 222 trillion liters of water were withdrawn in 2010 by thermoelectric power plants (Maupin and 

others, 2014), but not all of that water was consumed. As 

previously defined, water withdrawal refers to the amount of 

water extracted from a surface-water or groundwater source, 

and water consumption refers to that portion of withdrawn 

water that is evaporated or otherwise removed from readily 

accessible water resources. In the case of thermoelectric power 

generation, most water consumption occurs as evaporation 

from cooling systems. Cooling water that is not consumed 

typically is returned to the original water body. The amount 

of water consumed in a process is equal to the difference in 

the amount of water withdrawn and the amount returned. 

Thus, while thermoelectric power generation accounts for the 

largest total water withdrawals in the United States, its water 

consumption rate is much less than that of other uses such 

as irrigated agriculture (Solley and others, 1998; Kenny and 

others, 2009; Maupin and others, 2014). 

Water withdrawals for thermoelectric power generation 

vary by location and plant design. Eastern states accounted 

for about 86 percent of total withdrawals in 2010 (fig. 15) and 

75 percent of the related net power generation (Maupin and 

others, 2014). Most of these withdrawals are associated with 

thermoelectric power plants that use older, once-through cooling systems. Newer, wet recirculating cooling systems withdraw much less water. Most withdrawals for thermoelectric 

power are from surface water, but some southwestern States, 

where surface water is relatively scarce, tap groundwater for a 

substantial portion of their water withdrawals for thermoelectric power, including Nevada (89 percent), Arizona (74 percent), Utah (43 percent), and New Mexico (18 percent).

Concerns about water availability have led to greater use 

of degraded water sources for cooling and other thermoelectric 

power plant needs. Challenges in using these sources include 

the treatment needed to meet plant operation and regulatory 

discharge requirements and the potential for long transport 

distances from water sources. About 29 percent of total water 

withdrawals for thermoelectric power generation come from 

saline water along coastal areas, particularly California, 

Florida, and the Northeast (fig. 15). At least 50 power plants in 

the United States use treated municipal wastewater (reclaimed 

water) for cooling and other purposes; Florida and California 

have the largest number of plants that use reclaimed water 

(Veil, 2007).

The average amount of water withdrawn to produce a 

kilowatthour of electricity in the United States has decreased 

steadily from about 240 L in 1950 to about 72 L in 2010 (Maupin and others, 2014). This trend is attributed to decreased 

use of once-through cooling systems, more efficient cooling technologies, and increased thermal efficiency of power 

plants. Looking toward the future, electrical power consumption will likely increase, but freshwater withdrawals by power 

plants are projected to decrease as greater use is made of wet 
A. Freshwater withdrawals B. Saline-water withdrawals

EXPLANATION

Water withdrawals, in

 million liters per day 

0

1 to 7,571

7,572 to 15,142

15,143 to 22,712

22,713 to 34,069

34,070 to 42,397

0

500

1,000

1,500

2,000

2,500

1950 1960 1970 1980 1990 2000 2010 2020

Electricity generation, in billions of kilowatthours 

Year

Coal

Gas

Nuclear

Hydroelectricity

Other renewables

EXPLANATION

Water in Energy Production and Use 37

recirculating cooling systems (National Energy Technology 

Laboratory, 2011). 

Water Consumption—Carbon-Fuel and Nuclear Plants

Thermoelectric power plants consume large amounts of 

water, but exactly how much water is a matter of some uncertainty. Estimated rates of water consumption by power plants 

vary considerably (National Energy Technology Laboratory, 

2006; Macknick and others, 2011, 2012; Diehl, 2012; Diehl 

and others, 2013; Meldrum and others 2013; Diehl and Harris, 2014), largely because of a lack of standardized wateraccounting methods. Here we present a broad survey of values 

reported in the literature for water intensities for electricity 

generation at thermoelectric power plants. A much more 

detailed investigation based on thermodynamic constraints is 

provided by Diehl and Harris (2014) for power plant water 

intensities in 2010. 

Coal-fired power plants produce more electricity in the 

United States than any other type of plant—the 1.6 trillion 

kWh of electricity generated from coal in 2013 represents 

39 percent of total electricity generation in the country. The 

dominance of coal-fired plants in the United States, however, 

has declined in recent years (fig. 16) as more natural gas–fired 

plants have come on line. Steam turbines with once-through 

or recirculating cooling systems are used in most coal-fired 

power plants. Reported power plant water intensities for 

generating electricity from coal range from 0.2 to 1.2 L/kWh 

with once-through cooling and from 1.6 to 2.5 L/kWh with 

recirculating tower cooling (table 3). 

Natural gas-fired thermoelectric power plants generated 1.1 trillion kWh of electricity in 2013, about 27 percent 

of total electricity generation. No cooling is required for 

combustion turbines, so water consumption rates for these 

systems are negligible. Water consumption rates for gas-fired 

steam-turbine power plants are slightly greater than those for 

coal-fired systems, ranging from 0.7 to 1.7 L/kWh with once 

through cooling and from 2.1 to 4.2 L/kWh with recirculating 

tower cooling (table 3). Water consumption rates for natural 

gas combined-cycle power plants are generally less than those 

for gas-fired or coal-fired steam systems because of the higher 

thermal efficiency of combined-cycle systems; they range 

from 0.1 to 0.9 L/kWh with once-through cooling and from 

0.2 to 1.1 L/kWh with recirculating tower cooling.

Nuclear plants generate electricity with steam turbines, 

and the heat to produce the steam is provided by the splitting, 

or fission, of atoms of uranium-235. As of 2014, the 62 commercial nuclear power plants in the United States (fig. 17), 

comprising 100 reactors, were producing about 789 billion 

Figure 15. Freshwater and saline-water withdrawals for thermoelectric power generation by State, 

2010. (Modified from Maupin and others, 2014)

Figure 16. Annual electricity generation in the United 

States by fuel, 1950–2013. “Other renewables” include wind, 

biomass, geothermal, and solar power (U.S. Energy Information 

Administration, 2014b).

Continued on page 39
Explanation—Percentile classes

≤5 6–9 10–24 Insufficient

data for a

hydrologic

region

Low

Severe

hydrologic

drought

Moderate

hydrologic

drought

Below

normal

Extreme

hydrologic

event

Sunday, March 08, 2015

38 The Water-Energy Nexus—An Earth Science Perspective

Droughts and Energy Development

Drought is a protracted period of below-normal 

precipitation. The effects of drought vary with region, 

climate, and human activities. Extended periods of 

drought can cause streams and reservoirs to dry up and 

groundwater levels to decline. The resulting effects can 

be severe, including loss of agricultural crops, destruction 

of aquatic ecosystems, wildfires, and implementation of 

municipal water-use restrictions. Energy operations can 

also be adversely affected by droughts. 

Two things occur during droughts that can affect operations at thermoelectric power plants—reduced streamflow 

and increased stream temperature. Power production could 

be reduced as a result of limited water availability to satisfy 

all demands, including instream flow requirements. The 

drought of 2011 in Texas provides an example (Averyt and 

others, 2011). By late summer 2011, Texas had suffered the 

driest 10 months since record keeping began. Demand for 

electricity increased by 6 percent, which led to a 9 percent 

increase in water demand to produce this electricity (Scanlon and others, 2013). At the same time, storage in power 

plant cooling reservoirs decreased by 30 percent. The 

shores of Martin Creek Lake, the primary source of cooling 

water for the Luminant coal-fired power plant, receded 

to precariously low levels. In order to avoid a reduction 

in plant operations, a 14-km pipeline was constructed to 

import cooling water from the Sabine River (Scanlon and 

others, 2013). 

Power plant operating permits require that discharges 

of cooling water always be less than a certain maximum 

temperature in order to minimize adverse effects on fish 

and other aquatic life. Increased stream temperatures during 

droughts, combined with peak demands for electricity during summer months, can lead to situations in which plants 

must reduce power generation to avoid exceeding maximum discharge temperatures. During three summers from 

2007 to 2011, the temperature of the Tennessee River rose 

above a 32 °C threshold, forcing reductions in power output 

from the Browns Ferry nuclear power station. (Averyt and 

others, 2011). In the summer of 2012, one of two reactors at 

the Millstone nuclear power plant near New London, Connecticut, was shut down when temperatures in Long Island 

Sound, the source of the facility’s cooling water, reached 

their highest levels since the facility began monitoring in 

1971 (Eaton, 2012). Likewise, the high temperatures of 

the Mississippi River during a 2006 heat wave forced the 

Prairie Island nuclear plant in Minnesota to cut its electricity generation by more than half (Averyt and others, 2011). 

Electrical power grids in the United States have developed some resiliency over the years, and many new power 

plants are designed to consume less water than older plants. 

The droughts of recent years proved to be severe tests for 

electricity generators, but Americans received the power 

they demanded because providers were able to purchase 

electricity from alternative sources, albeit at higher costs 

for consumers.

Figure I–1. An example of a drought index map developed 

on the basis of percentile of 7-day average streamflow 

relative to historical streamflow on a given day of the year

(U.S Geological Survey, 2015). Other bases for drought indices 

include precipitation, such as the Palmer Drought Severity 

Index and the Standardized Precipitation Index (http://

droughtmonitor.unl.edu/), and soil and vegetation moisture 

(http://www.wfas.net/index.php/keetch-byram-index-moisture-

-drought-49).

The Browns Ferry nuclear power station in Tennessee was forced 

to reduce electricity generation for some summer months because 

of high water temperatures in the Tennessee River.
WISCONSIN

MINNESOTA

IOWA

NORTH

DAKOTA

SOUTH

DAKOTA

WYOMING

MONTANA

NEBRASKA

KANSAS

MISSOURI

ILLINOIS

INDIANA

OKLAHOMA ARKANSAS

TENNESSEE MISSISSIPPI

LOUISIANA

GEORGIA

KENTUCKY

TEXAS

NEW MEXICO

ARIZONA

NEVADA

CALIFORNIA

UTAH

COLORADO

IDAHO

OREGON

WASHINGTON

OHIO

WV 

VIRGINIA

NORTH

CAROLINA

SOUTH

CAROLINA

FLORIDA

PA

MD

NJ

DE

NEW YORK

VT

NH

MASS.

CT

RI

MAINE

ALABAMA

MICHIGAN

Shaded relief map 

by Tom Patterson

Water in Energy Production and Use 39

kWh of electricity per year, 19 percent of all electricity production in the country (Power Reactor Information System, 

2014). Electricity production from nuclear power plants has 

been fairly steady since 1996 when the most recent reactor 

came on line (fig 16). Production is predicted to remain fairly 

steady through 2035, at which time nuclear power will account 

for about 18 percent of electricity generation (U.S. Energy 

Information Administration, 2012b). Production will likely 

decline after 2035, as many nuclear power plants will be near 

the end of their expected lifetimes and few new plants are 

currently under construction. In spite of the 2011 Fukushima 

Daiichi nuclear disaster in Japan, polls still show modest public support for continued development of nuclear power in the 

United States (Newport, 2012). 

Water consumption rates for nuclear power plants range 

from 0.4 to 1.5 L/kWh with once-through cooling and from 

2.2 to 3.4 L/kWh with recirculating tower cooling, ranges 

similar to those of gas-fired steam-turbine plants (table 3). The 

nuclear power industry, however, has some additional, unique 

water needs, even if the amount of water used is relatively 

small. Nuclear fuel rods continually generate heat, even if 

electricity is not being produced. For this reason, cooling 

systems are designed to constantly remove this “decay heat” 

from the plant with water. In addition, when spent fuel rods 

are removed from nuclear reactors, they must be immersed for 

five years or more in deep pools of water for cooling and for 

blocking radiation (Alley and Alley, 2013).

There are many small biomass thermoelectric plants in 

operation in the United States. Wood-fueled thermoelectric 

plants are common in densely forested areas of the United 

States, such as New England. Plants fueled by other biomass 

sources are common in intensely farmed regions, such as the 

Central Valley of California. A total of about 60 billion kWh 

of electricity was generated from these plants in 2013, about 

1.5 percent of total electricity generation in the United States 

(U.S. Energy Information Administration, 2014b). The water 

intensity for generating electricity from biomass-fueled power 

plants is in the range of 1.8 to 3.6 L/kWh of electricity (Macknick and others, 2011), similar to that for coal-fired plants 

(table 3). 

Advances in technology will likely result in improved 

overall power-plant thermal efficiency in the United States 

as old plants are retired and new ones are brought online. 

However, pollution-control efforts at coal-, natural gas–, 

and biomass-fueled thermoelectric plants will affect thermal 

efficiency and, therefore, water consumption rates. Techniques 

Figure 17. Locations of the 100 operational commercial nuclear power reactors in the United States as of 2014. (World Nuclear 

Association, 2014)
Geothermal favorability

EXPLANATION

High

Low

0 200 400 KILOMETERS

0 200 400 MILES

WASHINGTON MONTANA

IDAHO

OREGON

WYOMING

UTAH

NEVADA

COLORADO

CALIFORNIA

ARIZONA NEW MEXICO ARIZONA NEW MEXICO

40 The Water-Energy Nexus—An Earth Science Perspective

for removing contaminants such as carbon dioxide, mercury, 

and sulfur from atmospheric emissions lead to cleaner air, but 

they also reduce thermal efficiencies of power plants. Methods for capturing carbon dioxide from power-plant emissions, 

although not yet fully developed, will inevitably lead to reductions in power-plant thermal efficiencies and increases in the 

water intensity of electricity generation (Meldrum and others, 

2013; Tidwell and others, 2013).

Water Consumption—Geothermal Plants

Geothermal energy is heat generated within the Earth’s 

core. Most of that heat is produced by radioactive decay of 

naturally occurring elements such as uranium, thorium, and 

potassium (Duffield and Sass, 2003). Heat flows outward from 

the core toward the land surface. The amount of heat flow is 

fairly uniform worldwide, but there are areas of anomalously 

high heat flow, such as in the vicinity of active or geologically 

young volcanoes. In areas of high heat flow, energy can sometimes be economically harvested for human use. The primary 

use of geothermal energy is to drive turbines and generate 

electricity in power plants that serve a large market. Secondary uses for geothermal energy include providing direct heat 

to buildings, sidewalks, and other infrastructure located near 

geothermal heat sources.

Geothermal energy sources produced about 17 billion 

kWh of electricity in the United States in 2013, about 0.4 percent of the Nation’s total electricity generation (U.S. Energy 

Information Administration, 2014b). Areas of current geothermal development in the United States are located within 

and to the west of the Rocky Mountains (fig. 18). On the basis 

of current technology, geothermal energy production in the 

United States is predicted to increase by about 4 percent annually through 2035 (U.S. Energy Information Agency, 2012b), 

although it will remain a relatively minor provider of electricity on the national scale.

Geothermal power plants extract hot geofluids2 from 

wells drilled as deep as several kilometers and use the heat 

of the fluids to power electrical generators. Three types of 

geothermal systems are used to generate electricity: dry steam, 

flash, and binary, depending on the nature of the geofluids 

(Duffield and Sass, 2003). Dry steam and flash techniques can 

2

The term “geofluid” denotes steam or saline groundwater; the term is used 

to distinguish these fluids from fresh groundwater. Consumption of geofluids 

is not included in the accounting of fresh water resources because of the high 

salinity.

The Palo Verde Nuclear Generating Station, located about 88 km west 

of downtown Phoenix, Arizona, is the largest nuclear power plant in 

the United States, serving approximately 4 million people. Located 

in the desert, Palo Verde is the only nuclear plant in the world that 

is not situated adjacent to a large surface water body. The facility 

evaporates water from the treated sewage of Phoenix and nearby 

municipalities to meet its cooling needs.

Figure 18. Relative favorability of occurrence of geothermal 

resources in the western contiguous United States. Identified 

geothermal systems are represented by black dots. (Williams and 

others, 2008)
Water in Energy Production and Use 41

be used when temperatures in the geothermal reservoir are 

generally between 175 and 300 °C; binary techniques usually are used when temperatures in the reservoir are less than 

200 °C. In dry steam systems, the geofluid is in the form of 

steam, and in flash systems, liquid geofluids pumped to the 

geothermal plant immediately flash to steam. The steam in 

both systems is used to directly drive a turbine that generates 

electricity. In a binary system, the geofluid temperature is not 

sufficient to vaporize water instantaneously; instead, a second 

fluid with a lower boiling point than water is vaporized to 

drive the turbine. The largest geothermal power plants in the 

United States use dry steam or flash techniques. 

The steam that passes through the turbines in dry steam 

or flash systems remains as steam or is condensed to liquid 

water; the steam is vented to the atmosphere, and any remaining condensate is injected back into the geothermal reservoir. 

Condensate may also be used for cooling, but in general these 

types of systems rely on dry cooling techniques. Fluids must 

be injected to the geothermal reservoir to maintain pressure, 

minimize induced seismic activity, and extend the life of the 

resource. Because about 70 percent of the original extracted 

geofluid mass is vented to the atmosphere as steam, this 

amount is typically made up with added water. Low-quality 

make-up water is acceptable for this purpose. For example, 

power plants at The Geysers geothermal field in northern California rely on treated municipal effluent for its make-up water. 

Small amounts of water are also needed at these plants for 

periodic flushing to avoid scale build up. Water intensity for 

California’s 10 flash power plants averages about 3.33 L/kWh 

of generated electricity (Adee and Miller, 2010).

Water consumption rates at binary geothermal plants vary 

depending on the technique used to cool the binary fluid after 

it has passed through the turbine. About 78 percent of binary 

plants within the United States rely on dry cooling (Mishra 

and others, 2011) and therefore consume water at rates similar 

to those of flash power plants. In hot summer weather, though, 

air cooling is inefficient; the power output of a binary plant 

can be reduced by as much as 50 percent of its wintertime output. As a result, some plant operators augment dry cooling systems with closed-loop wet recirculating cooling systems that 

use a combination of geofluid condensate and make-up water 

(often freshwater). Binary plants also require make-up for 

injection into the geothermal source, and because dry cooled 

plants operate at a lower thermal efficiency than water-cooled 

plants, more geofluids are extracted per kilowatthour of generated electricity and more make-up water must be injected. 

Water intensity for electricity generation at binary geothermal 

power plants with wet recirculating cooling systems has been 

reported to range from 6.8 to 9.9 L/kWh (table 3; Mishra and 

others, 2011).

Water Consumption—Concentrating Solar Power Plants

Concentrating solar power (CSP) technologies rely on 

the sun as a heat source, using mirrors to focus the sun’s 

energy on a small area. The technology has received considerable interest in recent years—30 States and the District of 

Columbia have established renewable portfolio standards that 

encourage the development of CSP technologies (U.S. Energy 

Information Administration, 2012c). In 2013, CSP plants in 

the United States generated about 926 million kilowatthours of 

electricity, much less than 1 percent of total electricity generation in the United States (U.S. Energy Information Administration, 2014a).

Most CSP technologies use mirrors to concentrate direct 

solar radiation onto a receiver tube in which a fluid is heated. 

The heated fluid is used to boil water for steam-driven turbine 

generators as in a traditional thermoelectric power plant. The 

heated fluid does not need to be used immediately; it can 

be stored and used to generate electricity at night or during 

cloudy weather. Unlike other types of thermoelectric power 

plants, a substantial amount of water is needed for the construction of CSP plants, in part because of the lower life span 

of CSP plants and the specialty chemicals that are required. 

Water consumption for plant construction is estimated at 

0.6 L/kWh (Meldrum and others, 2013). Water is also used 

for cooling purposes, just as with other thermoelectric plants. 

Water consumption rates for CSP plants depend largely on 

the type of cooling system that is used. For parabolic trough 

plants, water intensity is estimated to range from 2.1 to 

7.2 L/kWh (table 3; Meldrum and others, 2013). Parabolic 

trough CSP systems have operated in the California Mojave 

Desert for over 20 years.

Dish/engine or Stirling cycle CSP systems use a multimirrored dish that looks like a large satellite dish. The 

dish-shaped surface directs and concentrates sunlight onto a 

thermal receiver, which absorbs and collects the heat. This 

system uses the fluid heated by the receiver to move pistons 

and create mechanical power to run a generator or alternator to produce electricity. A distinct advantage of dish/engine 

The Geysers geothermal field in northern California is the only dry 

steam system in the United States. It produces more power (about 

950 MW on average) than any other geothermal plant in the world.
The Ivanpah Solar Electric Generating System in the Mojave Desert of California can produce up to 392 MW of electricity.

42 The Water-Energy Nexus—An Earth Science Perspective

systems is that they use dry cooling. Thus, no water is needed 

other than for mirror washing. Unlike the other CSP systems, 

however, dish/engine systems do not lend themselves easily 

to thermal storage, so these systems provide electricity only 

when the sun is shining (U.S. Department of Energy, 2009). 

Solar power is most effective in areas that have many 

hours of sunlight, such as the southwestern United States. 

Solar technologies such as CSP might improve power grid 

operations by providing energy when it is most needed during 

the hottest part of the day. It is estimated that CSP projects 

covering 1.4 percent of southwestern land could potentially 

generate as much power as is used in the entire United States 

(U.S. Department of Energy, 2009). Unfortunately, water is 

scarce in these same areas. In addition, some States such as 

California have placed restrictions on power-plant water use. 

As a result, CSP systems might require transport of water 

from distant sources, treatment of low-quality water such as 

municipal effluent, or use of dry or hybrid wet/dry cooling 

technologies.

Water Quality and Thermoelectric Power Plants

Water quality issues of electricity generation generally 

are related to contaminants emitted directly to the atmosphere 

from the fuel combustion, contaminants in the fuel residue that 

remains after combustion, and contaminants in water released 

to the environment. Power plants with once-through cooling systems place additional stress on water bodies and their 

ecosystems as a result of the temperature increases caused 

by return flows. Increased temperatures in streams can have 

deleterious consequences for aquatic life, especially during periods of drought when ecosystems are already stressed 

(Electric Power Research Institute, 2012). Large withdrawals 

for cooling also kill fish, larvae, and other organisms trapped 

against the intake structure (impingement) or drawn through 

the cooling system (entrainment). For steam-driven generators, 

the continual cycle of evaporation and condensation inside a 

boiler system leads to accumulation of salts and, therefore, 

a deterioration of water quality in boiler water. That water is 

occasionally flushed out, treated, and released to the environment (Diehl and Harris, 2014). The amounts of released boiler 

water are relatively small and generally have a minimal effect 

on water resources. Other issues are specific to fuel type.

Coal

Combustion of coal, gas, oil, and biomass emits carbon 

dioxide and other chemicals to the atmosphere. Carbon dioxide is a greenhouse gas that contributes to global warming. 

Other constituents that are released upon combustion, such 

as arsenic, mercury, sulfur oxides, nitrogen oxides, selenium, 

and additional trace elements, give rise to environmental and 

health concerns (see Box J—Energy, Atmospheric Emissions, 

and Water Quality). When gaseous or particulate pollutants 

are released to the atmosphere, surface-water and groundwater 

resources can be contaminated by rainfall or dry deposition. 
Water in Energy Production and Use 43

Many coal-fired power plants in the United States have 

installed pollution abatement systems such as dust collectors 

and flue-gas desulfurizers (FGD) or scrubbers to capture contaminants before they are released to the atmosphere. 

Power plants in the United States produced approximately 100 million metric tons of coal combustion residues in 

2012 (American Coal Ash Association, 2014), equivalent to 

about 13 percent of the total mass of coal consumed. Residues, often referred to as coal combustion products (CCPs) or 

simply coal ash, consist of fly ash, bottom ash, boiler slag, and 

compounds from FGD systems. Fly ash is the residue captured 

in smoke stacks upstream of scrubbers, bottom ash is the residue that accumulates in the bottom of the burner, boiler slag 

is bottom ash produced in a certain type of boiler (wet-bottom 

boilers), and FGD compounds are those that are captured by 

the scrubbers. Fly ash, bottom ash, and slag consist mostly of 

silicon, calcium, aluminum, and iron oxides (Electric Power 

Research Institute, 2010), but they often contain potential 

environmental contaminants such as arsenic, mercury, selenium, and uranium. The chemical nature of the ash relates to 

the type of coal (anthracite, bituminous, lignite), the location 

where it was mined, and the operating conditions of a plant. 

Flue gas desulferizer compounds consist of a number of products, the most prominent of which is gypsum.

About 47 percent of the combustion products generated annually in the United States are reused for a variety of 

purposes (American Coal Ash Association, 2014). Fly ash and 

bottom ash are used as additives for Portland cement, road and 

soil stabilizers, and bricks. Boiler slag is used for sandblasting 

and for traction control on ice- and snow-covered roads. Gypsum derived from FGD compounds can be used in wallboard. 

The remaining 53 percent of combustion products are placed 

in landfills or stored in water-filled impoundments near power 

plants. The U.S. Environmental Protection Agency recently 

issued new rules to promote the safe reuse, disposal, and storage of coal combustion products (U.S. Environmental Protection Agency, 2014a). The rules were developed in the wake 

of the 2008 spill of coal ash from an impoundment at a power 

plant in Kingston, Tennessee, that contaminated the Clinch 

and Emory Rivers (Ruhl and others, 2010). Cleanup costs for 

that spill exceeded 2 billion dollars. 

Natural Gas

Natural gas is referred to as a clean fuel in terms of the 

relatively low toxicity of its byproducts. Carbon dioxide is 

emitted when gas is burned, but the amount emitted is about 

half that from coal (see Box J—Energy, Atmospheric Emissions, and Water Quality). Natural gas, as it comes out of the 

well, can contain water, oil, gas condensates, hydrogen sulfide, 

mercury, and other potential contaminants, many of which 

have economic value. The gas is processed to remove these 

constituents prior to use. Nitrogen oxides can form from gas 

combustion, but again, emission rates are substantially less 

than those for coal (see Box J—Energy, Atmospheric Emissions, and Water Quality). There is no significant combustion 

residue to deal with. 

Nuclear

Water is essential for safe operation of today’s nuclear 

power plants. The legacies of environmental damage and 

water pollution left by disasters at Chernobyl, Ukraine (1986), 

and Fukushima, Japan (2011), where cooling water could 

not be adequately supplied and reactor cores melted, will last 

decades or more (Alley and Alley, 2013). However, nuclear 

power plants have the environmental benefit of emitting no 

greenhouse gases.

Leaks from reactor piping can contribute to contamination of cooling water. The Nuclear Regulatory Commission 

allows power plants to release radioactive constituents to the 

environment under normal operating conditions if the radioactivity is below permissible levels. Details of all such releases 

are available to the public through the Nuclear Regulatory 

Commission’s Agencywide Documents Access and Management System (ADAMS, http://www.nrc.gov/reading-rm/

adams.html). 

Spent fuel is also a potential source of water contamination; used fuel rods are stored in water baths to prevent them 

from overheating. Long-term disposition of spent nuclear fuel 

remains an unknown proposition in the United States. As of 

2014, a permanent repository for the used fuel has not been 

selected. Many criteria are involved in making decisions on 

locations for such a repository, but the most important one 

is isolation of the fuel rods from water and the biosphere for 

many thousands or even hundreds of thousands of years. The 

suitability of Yucca Mountain, located in the Mojave Desert in 

Nevada, as a permanent repository was studied for more than 

20 years by the U.S. Department of Energy, but the site was 

removed from consideration in 2009, prior to completion of 

the study (Alley and Alley, 2013).

Damage from the 2008 coal ash spill in Kingston, Tennessee.

Continued on page 47
Carbon dioxide

(84 percent)

Fluorinated

gases

(2 percent)

Nitrous oxide

(5 percent)

Methane

(9 percent)

44 The Water-Energy Nexus—An Earth Science Perspective

Energy, Atmospheric Emissions, and Water Quality

The burning of fuels to generate electricity, power 

motor vehicles, heat buildings, and power industry 

leads to the emission of volatile and particulate combustion products into the atmosphere. The types and amounts 

of emissions depend on the fuel (table J–1) and the design 

and operation of the combustion vessel. In terms of total 

mass, carbon dioxide is the largest pollutant. Other important pollutants include sulfur dioxide, nitrogen oxides, and 

mercury. Atmospheric emissions are tied to water quality in 

a number ways, including global climate, acid deposition, 

and the transport of mercury and other trace elements. 

Greenhouse gases, when present in the atmosphere, 

have the effect of increasing global temperatures. Carbon 

dioxide is the most prominent greenhouse gas (fig. J–1); 

other important greenhouse gases include methane, nitrous 

oxide, and fluorinated gases such as sulfur hexafluoride. 

The effect of a greenhouse gas on global climate depends 

on its atmospheric concentration, its heat absorbing 

capability (usually expressed in units of carbon dioxide 

equivalent), and the rate at which the compound decays or 

is removed from the atmosphere. Atmospheric concentrations of carbon dioxide have been increasing since the first 

measurements were made at Mauna Loa, Hawaii (fig. J–2) 

in the late 1950s. The increased concentrations are attributed to human activity, in particular energy consumption; 

combustion of fossil fuels accounted for 94 percent of 

total carbon dioxide emissions in the United States in 2011 

(U.S. Environmental Protection Agency, 2013b). Energy 

operations in general, including release of methane from 

natural gas and oil wells, accounted for 86 percent of total 

greenhouse gas emissions in 2011 (U.S. Environmental 

Protection Agency, 2013b). Climate change affects many 

aspects of water availability and quality, including changes 

in precipitation and evapotranspiration patterns, possibly 

more intense storms, altered 

ecosystems, and sea-level rise. 

For a more in-depth discussion of climate change and its 

effects on water and energy 

resources, see the section 

“Science for Addressing the 

Water-Energy Nexus.”

Acid deposition (sometimes referred to as acid 

rain) is precipitation or dry 

atmospheric fallout that is 

acidic in nature; that is, it 

has a high concentration of 

hydrogen ions and a low 

pH value (U.S. Geological 

Survey, 2014a). Acid deposition can lead to the acidification of lakes and streams 

and can have deleterious 

effects on ecosystems, such 

as fish kills. Acid deposition 

occurs when sulfur dioxide 

and nitrogen oxides in the 

atmosphere are converted to sulfuric and nitric acid, respectively. Sulfur dioxide and nitrogen oxides are emitted naturally 

to the atmosphere by volcanic activity, but human activity, 

especially the combustion of coal, gasoline, and other fossil 

fuels (table J–1), is the primary source of atmospheric stores 

of these compounds. Laws and rules enacted over the past few 

decades for controlling emissions of these compounds (such 

as requirements for catalytic converters in motor vehicles and 

flue-gas desulfurization systems in power plant smokestacks) 

have resulted in a substantial decrease in acid deposition in the 

United States since 1985 (fig. J–3). 

Figure J–1. Relative 

contributions to the total 

greenhouse gas emissions 

for the United States, 2011, 

as a percentage of the 

total emissions of 6.7 billion 

metric tons of carbon dioxide 

equivalent. (U.S. Environmental 

Protection Agency, 2013b)

Table J–1. Gaseous and particulate emissions from the uncontrolled combustion of common 

fossil fuels. Hard coal refers to bituminous and subbituminous coal.

[Values are in grams per kilowatthour of thermal energy. NOx, nitrogen oxides; <, less than]

Pollutant Hard coal Lignite Fuel oil Wood Natural gas

Carbon dioxide 1

340 1364 1279 2302 1202

Sulfur dioxide 1

2.75 14.90 14.86 20.04 1<0.0

NOx

1

1.05 10.66 10.70 20.76 10.34

Carbon monoxide 1

0.32 10.32 10.06 20.93 10.05

Particulate matter 1

4.33 111.7 10.06 20.62 1<0.01

Mercury 2

5.0×10-6 21.0×10-5 21.1×10-6 25.4×10-6 (

3

)

1

European Environmental Agency (2008).

2

U.S. Environmental Protection Agency (variously dated).

3

Mercury is removed from natural gas during processing.

The combustion of 

fossil fuels, primarily coal, 

for the generation of electricity accounts for close 

to 70 percent of all atmospheric mercury produced 

by humans in the United 

States (Engle, 2005). Atmospheric mercury follows a 

complex pathway of possible 

reactions including deposition, re-emission, oxidation, 

reduction, methylation, and 

bioaccumulation. Elemental 

mercury, the dominant form 

of atmospheric mercury, has 

only limited solubility and 
Emission from matural 

and anthropogenic 

Sources

RGM & Hg-p

Elemental Hg

Oxidation to RGM and

Hg-p via reaction with

oxidants (e.g., O3, OH.

)

Dep. of RGM and Hg-p

Deposition of RGM and Hg-p

Re-emission

Re-Emission and Deposition

Evasion

Inorganic Hg

Net mercury methylation at the watersediment interface by microbial

and chemical mechanisms

MeHg

bioaccumulation

and 

biomagnification MeHg

Dep. of Elemental Hg

300

310

320

330

340

350

360

370

380

390

400

1955 1965 1975 1985 1995 2005 2015

Carbon dioxide concentration, in parts per million 

Year

4.5

Greater than or 

equal to 5.7

Laboratory pH (standard units)

EXPLANATION

4.9

5.3

Less than or equal to 4.1

A

B

Water in Energy Production and Use 45

Figure J–4. Environmental pathways for mercury (Hg) emitted to the atmosphere and 

potential for uptake and bioaccumulation in aquatic organisms. (RGM, reactive gaseous 

mercury; Hg-p, particulate bound mercury; MeHg, methylmercury; O3

, ozone; and OH-, 

hydroxyl radical) (From Engle, 2005)

Figure J–3. Average annual pH values in precipitation 

for (A) 1985 and (B) 2012 indicate a substantial reduction 

in acid deposition over this period. (National Atmospheric 

Deposition Program, 2014)

Figure J–2. Mean annual atmospheric carbon 

dioxide concentrations as measured at Mauna 

Loa, Hawaii, 1959–2013. (National Oceanic and 

Atmospheric Administration, 2013)

reactivity, allowing for long travel distances before it reenters 

the surface environment (fig. J–4). Mercury causes problems 

in many ecosystems. For example, fish and other aquatic biota 

can bioaccumulate organic forms of mercury (derived from 

the methylation of elemental 

mercury), rendering them unfit 

for human consumption. Fish 

advisories in many parts of the 

United States have been linked 

to atmospheric deposition of 

mercury (Cocca, 2001). The 

emission of mercury from power 

plants can be controlled though 

a variety of technologies. In a 

typical plant burning bituminous 

coal in conjunction with fabric 

filters and flue-gas desulfurization 

systems, roughly 60 percent of 

the original mercury is removed, 

and the remaining 40 percent 

is emitted to the atmosphere 

(Kolker and others, 2006). 

Despite available technology, 

approximately 40 percent of the 

roughly 1,400 coal and oil-fired 

generating units in the United 

States do not use advanced pollution controls (U.S. Environmental 

Protection Agency, 2013b).
NOT TO SCALE Illustration by Douglas W. Duncan and Eric A. Morrissey

Seal formation

EXPLANATION

CO2 flow

Carbon dioxide (CO2) storage volume Gas flow

Storage formation

Gas

Oil and gas flow Oil

Fault—Arrow indicates relative movement

46 The Water-Energy Nexus—An Earth Science Perspective

Carbon Capture and Sequestration

To limit carbon emissions and climate change, carbon dioxide (CO2

) can be captured from large stationary sources, such as coal-fired power plants, compressed to a liquid state, and injected deep underground 

into permeable geologic strata (Duncan and Morrissey, 

2011). Potential storage formations include deep saline 

formations, depleted oil and gas reservoirs, and coal seams 

that are not considered economically viable for mining. The 

technology for sequestering CO2 is still being developed. 

On a smaller scale, CO2 has been injected into geologic 

formations for many decades as part of enhanced oil recovery efforts in the United States, but as of 2014, the United 

States had no commercial geologic carbon sequestration 

systems in operation. Two sequestration systems, however, 

are operational in Norway, as well as one in Algeria (Global 

CCS Institute, 2013). These systems do not involve CO2

capture at power plants. Instead, the injected CO2 is an 

unwanted byproduct of natural gas extraction. 

Geologic carbon sequestration faces many challenges. 

To be viable as a strategy for reducing greenhouse gases, 

vast amounts of carbon dioxide would need to be stored in 

geologic formations. The geologic formations into which the 

fluid is injected must be sufficiently porous and permeable 

and must be overlain by layers of impermeable rock to store 

and isolate the CO2

 for long periods of time. A key challenge 

for carbon sequestration is to avoid affecting current or future 

underground sources of drinking water. One potential adverse 

effect of sequestration is the displacement of saline water into 

freshwater-bearing horizons; another is the escape of carbon 

dioxide to shallower water horizons, which could cause acidification of groundwater and mobilization of trace elements. 

Improperly abandoned or damaged oil and gas wells are an 

important concern because they can provide short circuits back 

to the biosphere.

Carbon capture will lead to increased water withdrawal 

and consumption rates at coal- and natural gas–fueled thermoelectric power plants. Additional water requirements are 

associated with capture and compression of CO2

. In addition, 

carbon capture systems reduce power-plant thermal efficiency, 

so more water will be required for cooling and fuel processing. 

Figure K–1. The concept of geologic carbon sequestration. (From Duncan and Morrissey, 2011)
Water in Energy Production and Use 47

Biomass

Biomass power plants have become popular since 2000 

as green alternatives to fossil fuel–based power plants. Combustion of biomass, however, as with fossil fuels, is accompanied by the release of particulates and gases, including carbon 

dioxide, nitrogen oxides, volatile organic compounds, and 

sulfur compounds, into the atmosphere (table J–1). Biomass 

combustion can be viewed as being carbon neutral because the 

organic matter would eventually decompose and emit the same 

amount of carbon, but because coal-fired power plants are 

more efficient than biomass plants (table 3), carbon dioxide 

emissions for wood are about 30 percent more than those for 

coal per kilowatthour of generated electricity. 

The exact amount of additional water required is 

not known. Estimates of increased withdrawal and 

consumption rates are as high as 90 and 75 percent, 

respectively (Meldrum and others, 2013). Ongoing 

research and development by the U.S. Department of 

Energy and others is seeking ways to reduce this water 

consumption penalty. 

Identifying potential geologic storage formations and determining the amount of CO2

 that can be 

sequestered on a national basis are important for longterm planning. The U.S. Geological Survey recently 

completed an evaluation of the technically accessible 

storage resource for CO2

 for 36 sedimentary basins in 

the onshore areas and State waters of the United States 

(U.S. Geological Survey, 2013). The estimated mean 

storage capacity was approximately 3,000 metric gigatons of CO2

, roughly 500 times the 2011 annual energyrelated CO2

 emissions for the United States (U.S. Geological Survey, 2013). The estimate was determined by 

using a probabilistic approach based on current geologic 

and hydrologic knowledge of the subsurface and current 

engineering practices. As illustrated in figure K–1, CO2

storage occurs by two mechanisms—buoyant trapping 

and residual trapping. In buoyant trapping, the formation pore space is filled with CO2

 and is held in place by 

seal formations on the top and sides of the porous rock. 

Buoyant trapping is analogous to the mechanism by 

which oil and gas are naturally trapped in conventional 

subsurface reservoirs and is illustrated in the figure 

by the accumulation of CO2

 in arc-shaped structures 

(anticlines) that are overlain by low-permeability seal 

formations. Residual trapping occurs as injected CO2

passes through the storage formation and leaves some 

CO2

 behind; the CO2 is held in place by surface tension 

in pore spaces. Residual trapping accounts for 98 percent of the estimated CO2

 storage capacity; however, 

depleted conventional oil and gas reservoirs with large 

capacities for buoyant trapping might be favored locations for CO2

 storage because of the accrued knowledge 

of these systems (U.S. Geological Survey, 2013). 

Long-term success of any geologic carbon sequestration or wastewater injection operation also depends 

on a full understanding of the physical and chemical 

interactions among injected fluids, formation groundwater, and formation minerals (Kharaka and others, 2009). 

Processes such as dissolution and precipitation can alter 

rock porosity, thereby changing the amount of available storage space. Injection pressures that are too great 

can induce seismic activity or possibly fracture rocks 

and create unintended pathways for fluid migration (see 

Box H—Subsurface Fluid Injection).

View to the south of Yucca Mountain crest. Yucca Mountain was once 

considered as a repository for high-level nuclear waste.

Ethanol plant in South Dakota.
48 The Water-Energy Nexus—An Earth Science Perspective

Construction of Hoover 

Dam between 1933 and 

1935 used 3.33 million m3

of concrete, requiring 

about 2 billion L of 

water. Although this is 

a substantial quantity of 

water, it is equivalent to 

less than 1 percent of 

the amount of water that 

evaporates from Lake 

Mead each year (Moreo 

and Swancar, 2013).

Hydroelectric Power Plants

Hydroelectric power refers to electricity produced from 

the gravitational force of falling water. Hydroelectric plants 

produced approximately 269 billion kWh of electricity in the 

United States in 2013, representing about 7 percent of total 

electricity generated in the country (U.S. Energy Information 

Administration, 2014b). Hydroelectric power is more important on a global scale, accounting for approximately 19 percent 

of electrical power worldwide. 

The water intensity of hydroelectricity is more problematic to estimate than that of electricity generated at thermoelectric power plants. Water consumption for generation of 

hydroelectricity consists of evaporation that occurs from 

reservoirs that feed hydroelectric plants. Hence, calculations 

of water intensities require estimates of evaporation rates. In 

addition, many dams are constructed for multiple purposes, 

such as municipal, agricultural, and industrial water supply; 

navigation; flood control; and recreation; as well as generation of hydroelectricity. No commonly accepted methodology 

exists for determining how much reservoir evaporation should 

be attributed to hydroelectricity, or other specific reservoir 

uses (Bakken and others, 2013). If a dam were constructed 

specifically for the generation of hydroelectricity, it may be 

appropriate to attribute all of the evaporative loss from a reservoir to generation of electricity. Many dams in the western 

United States were constructed specifically for irrigation water 

supply, with hydroelectric plants installed many years later; 

evaporation from these reservoirs is perhaps best assigned 

entirely to irrigation. 

Reservoir water consumption rates can be expressed as

Qop = (ET0—ET)*A (1)

where

Qop is annual operational consumption of water, in 

cubic meters per year; 

ET0 is the evaporation rate of open water, in 

meters per year; 

ET is the estimated evapotranspiration rate of the 

impounded area prior to being inundated; 

in meters per year; and 

A is the surface area of the reservoir, in square 

meters. 

Evapotranspiration refers to the combined evaporation from 

open water surfaces, soil, and plants. Equation 1 does not 

account for water moving from the reservoir to the underlying 

groundwater system; this water is not considered consumed 

water because it is theoretically still available for use.

Evaporation and evapotranspiration rates depend on 

weather patterns, air temperatures, and solar radiation. Evapotranspiration rates also depend on vegetation and available 

soil-water content; if the supply of soil water is unlimited, as 

occurs in many humid regions, then ET values should be very 

similar to those of ET0

. In arid regions, ET is substantially 

less than ET0. Because hydroelectric plants are located in all 

parts of the country, water consumption rates for generation 

of hydroelectricity vary across the United States. There is no 

nationwide network for monitoring reservoir evaporation; 

however, consumption rates for hydroelectric plants located in 

humid settings should be less, in general, than those for plants 

located in arid regions, assuming similar dam and reservoir 

characteristics. 

As an example, we calculate the water intensity for a 

hydroelectric system in the northern Cascade Mountains of 

Washington. The Skagit River Hydroelectric Project was built 

to supply electricity to the city of Seattle. The project contains 

three dams that generate about 2.1 billion kWh/yr. The three 

reservoirs in the project have a combined surface area of about 

52 km2 and are located in a humid region with annual precipitation of about 1.468 m and annual ET0

 of about 0.648 m (calculated from average pan evaporation of two nearby National 

Weather Service sites). Application of equation 1 with ET

assumed to be 0.508 m/yr (Drost and Lombard, 1978) indicates that annual water consumption for the three reservoirs is 

about 7.3 billion liters. Because this project was constructed 

specifically for hydroelectricity generation, it is reasonable to 

assign all water consumption to that purpose. Thus, the water 

intensity for hydroelectricity from the Skagit River Hydroelectric Project is calculated to be about 3.5 L/kWh, a value 

somewhat greater than water intensities for most other forms 

of electricity generation (table 3). 

The design of the Skagit River Hydroelectric Project and 

its location in a humid setting, where the reservoir waterconsumption rates are relatively low, imply that the calculated 

water intensity of 3.5 L/kWh is less than that of most other 

large hydroelectric plants in the United States, at least those 

plants associated with reservoir-dam systems designed exclusively for the generation of hydroelectricity. We do not attempt 

to estimate a maximum water intensity for hydroelectricity 

because of the complexities involved and lack of available 

data. The average water intensity for hydroelectricity in the 

United States was estimated to be 69 L/kWh of electricity by 

Torcellini and others (2003). That estimate is unrealistically 
Water in Energy Production and Use 49

high because the study assigned all reservoir evaporation 

to the generation of hydroelectricity and invoked a uniform 

assumption that ET in equation 1 was equal to 0. If that value 

of 69 L/kWh were correct, then the amount of water consumed 

for the generation of hydroelectricity would substantially 

exceed the total combined water consumption for all other 

forms of electricity generation in the United States on an 

annual basis. Accurate determination of average water intensity for hydroelectricity in the United States cannot be made 

until a standardized methodology is developed for apportioning reservoir evaporation among various reservoir uses.

Pumped-storage hydroelectric systems provide a unique 

and important form of energy storage in some parts of the 

United States. The systems consist of reservoirs above and 

below a traditional dam and a series of pumps that can 

transport water from the lower to the upper reservoir. These 

systems operate at a net energy loss (about 20 to 40 percent 

more energy is required to pump the water up than is obtained 

from water flowing through the dam), but they help to balance daily variations in energy loads. Demands for electricity 

fluctuate throughout the day, with the highest demands during 

daylight hours and the lowest demands at night. The strategy 

for pumped systems is to pump water to the upper reservoir 

during the nighttime when electricity demand and price 

are low; the water can then be released to pass through the 

hydroelectric plant during peak-demand times. Pumped storage is the largest energy storage system within the U.S. power 

grid; electrical generating capacity was about 21 GW in 2013 

(National Hydropower Association, 2013). 

Hydroelectric plants have several beneficial features: no 

fuel is required, very little in the way of greenhouse gases or 

other waste products is generated, and power can be quickly 

ramped up or down to meet ever changing energy demands. 

Dams change the natural course of rivers, however, and can 

have adverse effects on aquatic ecosystems (Collier and 

others, 1996), such as disruption of natural aquatic habitats, 

elimination of sediment flows below dams, entrainment and 

impingement of fish and other aquatic life in turbines, and 

alteration of natural temperature and oxygen levels in streams. 

As an example, dams that were built in past decades on the 

Columbia River in Washington have cut off salmon and other 

fish from more than 1,700 km of natural spawning habitat 

(Northwest Power and Conservation Council, 2010). Dam 

construction in the United States has slowed considerably 

in recent years, largely because of concerns for ecosystems. 

However, hydroelectric generating capacity continues to 

expand with addition of generators to existing non-powered 

dams and conduits. 

Wind and Passive Solar

Water requirements for wind and passive solar energy 

development are generally low. Relatively small amounts of 

water may be needed for construction and installation of wind 

turbines, and the construction of solar panels consumes the 

equivalent of about 0.3 L/kWh (Meldrum and others, 2013). 

Once wind turbines and solar panels begin generating electricity, the only water-related issue is the need for water to 

periodically clean turbine blades and solar panels.

Summary Water Requirements—Electricity and 

End-Use Sectors

Energy use can be partitioned into electrical power 

generation and four end-use sectors: transportation, industrial, 

residential, and commercial (fig. 19). Electricity generation 

accounts for about 40 percent of all energy consumption in 

the United States, more energy than is used directly in any 

individual end-use sector. Electricity is an intermediate form 

of energy, and the energy consumed in generating it can be 

apportioned to the end-use sectors on the basis of electricity 

use. For each sector, primary and total energy consumption 

can be determined. Primary consumption (fig. 19) is the direct 

use of an energy source, such as the use of natural gas to heat 

homes or the use of gasoline to power cars. Total energy consumption (fig. 20) includes primary energy consumption and 

the energy required to provide the electricity that is used by 

each sector. In the discussions that follow, energy consumption 

for the use sectors is provided in terms of both primary and 

total consumption.

Figure 19. Primary energy 

consumption in the United 

States for electricity 

generation and four end-use 

sectors, 2013, as a percentage 

of the total consumption of 

28.5 trillion kilowatthours of 

thermal energy. (U.S. Energy 

Information Administration, 

2014b.)

Figure 20. Total energy 

consumption for the United 

States by end-use sector, 

2013, as a percentage of 

the total consumption of 

28.5 trillion kilowatthours of 

thermal energy. (U.S. Energy 

Information Administration, 

2014b.)

Electric power

(39 percent)

Residential

(7 percent)

Commercial

(4 percent)

Industrial

(22 percent)

Transportation

(28 percent)

Residential

(22 percent)

Commercial

(18 percent)

Industrial

(32 percent)

Transportation

(28 percent)
50 The Water-Energy Nexus—An Earth Science Perspective

Direct use of energy often involves little in terms of water 

requirements. Flipping the switch of a house light, adjusting 

a room thermostat, and driving a car to work are actions that 

outwardly require no direct water use; however, as shown in 

the preceding sections, water is consumed by almost all stages 

of delivering that electricity to the house or that gasoline to 

the filling station. The end-use sectors provide a convenient 

framework for analyzing the amount of water consumed for 

energy-related functions.

Total water consumption for each end-use sector is 

determined by summing the requirements for each phase of 

energy production and use including fuel extraction or growth, 

fuel processing and transportation, generation of electricity, 

and end use. As with energy consumption, water consumption 

for electricity generation can be assigned to specific end-use 

sectors. A general lack of site-specific data and the large variability in processing techniques make it difficult to accurately 

quantify all energy-related water consumption on a national 

scale, but water consumption for the different end-use sectors 

can be discussed in terms of ranges of estimated values.

Water-quality issues associated with energy production 

and use are more difficult to summarize than water consumption. Unlike water consumption, the water-quality issues 

addressed in previous sections cannot simply be added up on a 

use-sector basis. Water-quality issues related to the generation 

of electricity were addressed in the previous section, and, in 

general, the end use of electricity does not introduce additional 

issues. Water-quality issues associated with primary energy 

consumption in the transportation, residential, and commercial 

use sectors are related to possible leaks during transport and 

storage of fuels and atmospheric emissions of carbon dioxide 

and other pollutants (see Box J—Energy, Atmospheric Emissions, and Water Quality). Water-quality issues associated 

with the industrial-sector energy use cannot be fully assessed 

because of the general lack of information on processes in 

this sector and because not all water used in this sector is tied 

to energy.

Electricity

The total water intensity of producing one kilowatthour 

of electricity is calculated by adding the water intensity for 

extracting and processing the fuel that is used in generating 

that electricity and the water intensity of the electrical power 

plant. Water consumption rates for extraction and processing of fuel were previously given in terms of water volume 

per unit mass or volume of fuel (table 1). These rates can be 

converted to water intensities in units of liters of water per 

equivalent kilowatthour of electricity by accounting for fuel 

energy content and power-plant thermal efficiency. Total water 

intensities for the generation of electricity by different fuels 

and types of power plants and cooling systems are presented in 

table 4, which combines the water intensities of power plants 

(table 3) with those for extraction and processing (table 1). 

Figure 21 shows the range of the total annual water consumption for electricity generation in the United States for 2013 

estimated on the basis of the given water intensities.

Total water intensity for producing electricity by steam 

turbine appears to be slightly less for coal-fired power plants 

than for nuclear and natural gas–fired power plants with 

identical cooling systems (table 4). Combined-cycle natural gas power plants are less water intensive than gas steam 

plants. Generation of electricity at hydroelectric, geothermal, 

or concentrating solar power plants (all renewable sources) is 

more water intensive than generation of electricity at fossilfuel power plants. Wind and passive solar power plants have 

essentially negligible water intensities. 

Estimates of annual water consumption for all electricity generation in the United States in 2013 range from 4.1 to 

9.5 trillion L/yr (table 4, fig. 21). These estimates are derived 

from data in published reports. The broad range illustrates 

the large uncertainty inherent in determining a nationwide 

consumption rate. Thermoelectric power plants account for 

most of the water consumed in the generation of electricity. 

Diehl and Harris (2014) provide a detailed analysis of water 

withdrawal and consumption rates at 1,290 individual power 

plants in the United States. The cumulative consumption for 

those plants in 2010 was about 4.8 trillion L (Diehl and Harris, 

2014); those authors caution that any estimate of water consumption at the national scale could be in error by 20 percent 

or more. The estimated consumption rate for the generation 

of hydroelectricity (900 billion L/yr) should be considered a 

minimum value because of difficulties previously described. 

The uncertainty in consumption estimates reflects a lack of 

site-specific data as well as limitations of estimation methods. 

This uncertainty clouds our current understanding of water use 

at power plants and complicates efforts to predict future water 

needs for generating electricity. 

Water consumption for generation of electricity is just a 

fraction of the 222 trillion L that were withdrawn by thermoelectric power plants in 2010. The range in total water 

consumption given in table 4 is equivalent to 2 to 4 percent of 

water withdrawn by power plants in 2010. Per capita electrical use in the United States was approximately 12,400 kWh 

for 2013, equivalent, in terms of thermal energy, to about 

36,000 kWhth. Associated annual water consumption for generation of electricity was in the range of 13,000 to 30,000 L 

per capita.

The U.S. Energy Information Administration allocates 

electricity use to the four end-use sectors on the basis of sales. 

For 2013, residential customers used 38 percent of generated 

electricity, commercial customers used 36 percent, industry 

accounted for 26 percent, and transportation used a negligible 

amount (0.2 percent) (U.S. Energy Information Administration, 2014b). Water consumption for electricity can likewise be 

allocated to specific end-use sectors, and total energy-related 

water consumption can be tallied for each sector. 
Water in Energy Production and Use 51

Table 4. Estimates of water consumption in the United States for different types of electricity generation in terms of water intensity (in 

liters of water per kilowatthour of generated electricity) and in terms of total water consumed in 2013.

[L/kWh, liters of water per kilowatthour of electricity; yr, year; na, not applicable; ~, approximately]

Plant type Cooling 

process

Water consumption 

rate for fuel 

extraction/processing 

(L/kWh)

Power plant 

water consumption rate1

(L/kWh)

Total water 

consumption 

rate 

(L/kWh)

Annual 

electricity 

generated2

(trillion kWh/yr)

Annual water 

consumption 

(trillion L/yr)

Coal Once-through 3

0.03–0.19 0.2–1.2 0.2–1.4

1.57 7

1.5–3.3

Tower 3

0.03–0.19 1.6–2.5 1.6–2.7

Nuclear Once-through 4

0.05–1.2 0.4–1.5 0.5–2.7

0.79 7

1.1–2.8

Tower 4

0.05–1.2 2.2–3.4 2.3–4.6

Natural gas steam Once-through 3

0.09–1.2 0.7–1.7 0.8–2.9

1.01 8

0.4–2.2

Tower 3

0.09–1.2 2.1–4.2 2.2–5.4

Natural gas combined 

cycle

Once-through 3

0.07–0.9 0.1–0.9 0.2–1.8 

Tower 3

0.07–0.9 0.2–1.1 0.3–2.0

Biomass Tower ~0 1.8–3.6 1.8–3.6 0.03 0.1 

Geothermal steam (binary) Tower na 6.8–9.9 6.8–9.9 0.02 0.1–0.2

Concentrating solar 

(parabolic trough)

Tower 5

0.6 2.1–7.2 2.7–7.8

0 0

Dry 5

0.6 40.1–0.5 0.7–1.1

Hydroelectric6 na na 3.5 3.5 0.27 0.9

Wind na na ~0 ~0 0.17 0

Total na na na na 3.90 4.1–9.5

1

From table 3.

2

U.S. Energy Information Administration (2014a).

3

From table 1.

4

Meldrum and others (2013).

5

For plant construction (Meldrum and others, 2013).

6

Value for hydroelectric power is for reservoir evaporation from example in this report. It should be considered a minimum value. As described in the text, 

average and maximum water intensities for generation of hydroelectricity cannot be determined because of a lack of standardized methodology and data.

7

Assumes percentages of once-through and tower cooling from Diehl and Harris (2014).

8

Includes both natural gas steam and combined cycle; assumes percentages of once-through and tower cooling from Diehl and Harris (2014).

Figure 21. Estimated range of water consumption for the 

generation of electricity in the United States by method 

of generation, 2013. The estimated consumption rate for 

generation of hydroelectricity (900 billion liters per year) 

should be considered a minimum value. As described in the 

text, average and maximum consumption rates for generation 

of hydroelectricity cannot be estimated because of a lack of 

standardized methodology and data. 

Water consumption, in trillions of liters

0

1

2

3

4

GeothermalHydroelectricNatural Nuclear Biomass

gas

Coal Wind/

solar
52 The Water-Energy Nexus—An Earth Science Perspective

Transportation

Transportation of people and commodities by car, truck, 

bus, boat, train, and airplane accounted for 28 percent of all 

energy consumption in the United States in 2013. Oil products 

represent about 93 percent of all transportation fuels, and biofuels account for a relatively small proportion of transportation 

fuels (about 4.5 percent). Water requirements for production 

and refinement of these fuels, as described previously, are 

summarized in table 5 and figure 22. 

The large contribution of irrigated biofuel crops to overall 

water consumption in the transportation sector is noteworthy. 

The estimated range of water consumption for all transportation fuels is 6.5 to 9.1 trillion L/yr. Biofuels may account for 

38 to 54 percent of that consumption, even though biofuels 

are just a small fraction of all transportation fuels. Irrigation 

of corn and soybean crops results in high water consumption 

rates for the production of bioethanol and biodiesel relative to 

the production of hydrocarbon fuels. Bioethanol and biodiesel 

also have less energy content than gasoline and diesel fuel 

(table 2). Flexible fuel vehicles operating on E85 typically see 

a drop in fuel economy (kilometers per liter) of 25 to 30 percent relative to that of gasoline (U.S. Department of Energy, 

2012). Therefore, when water intensity is determined on a 

fuel-economy basis, biofuels consume even more water. 

On a per capita basis, Americans consume about 2,800 L 

of gasoline or other transportation fuels each year, equivalent, in terms of thermal energy, to about 25,000 kWhth

(U.S. Energy Information Administration, 2014b). Estimated 

annual water consumption for transportation fuels in the 

United States is between 20,000 to 29,000 L per person, 

equivalent to about 55 to 79 L of water per day. If only 

hydrocarbon-based fuels were used for transportation, the 

associated range of per capita water consumption would shrink 

to about 9,000 to 17,000 L/yr (25 to 45 L/d).

Table 5. Estimates of water consumption in the United States for different types of transportation fuels in terms of rates of 

consumption (in liters of water per liter of fuel) and in terms of total water consumed in 2013.

[Water consumption rates for natural gas are given in L/kWhth. L, liter; kWhth, kilowatthours of thermal energy; --, unknown; na, not applicable]

Fuel type

Water 

consumption for 

fuel production 

or growth 

(L/L)

Refinery 

water 

consumption 

(L/L)

Total water 

consumption 

(L/L)

Percentage 

of total 

transportation 

fuels1

Annual energy 

consumed for 

transportation 

in 20131

(trillion kWhth)

Annual water 

consumed for 

transportation 

fuels in 2013 

(trillion L)

Oil products 2

2.1–5.1 21.5 3.6–6.6 92.5 7.31 3.0–5.5

Bioethanol 3

56 32.3 58.3 3.9 0.31 3.2

Biodiesel 4

57 41–3 58–60 0.6 0.05 0.3

Natural gas -- -- 5

0.03–0.4 L/kWhth 2.9 0.23 0–0.1

Gasoline from oil sands 6

0.4–5.8 21.5 1.9–7.3 0 0 0

Gasoline from oil shale 7

0.8–11.1 11.5 2.3–12.6 0 0 0

Gasoline from coal -- -- 8 5–7.3 0 0 0

Total na na na 100 7.90 6.5–9.1

1

U.S. Energy Information Administration (2014a).

2

Wu and others (2009), and Wu and Chiu (2011).

3

This report and Mueller (2010).

4

This report, Pate and others (2007), and National Research 

Council (2008).

5

From tables 2 and 4.

6

Moorhouse and others (2010).

7

Government Accountability Office (2010).

8

U.S. Department of Energy (2006).

Biofuels make up about 5 percent of transportation fuels in the United 

States, but they may account for more than 50 percent of all water 

consumed for transportation fuels.
Water consumption, in trillions of liters

0

1

2

3

4

5

6

Oil products Bioethanol Biodiesel Natural gas

Water in Energy Production and Use 53

Industrial

The industrial sector, comprising petroleum, chemical, 

paper, food, mineral, mining, and other industries, accounted 

for about 32 percent of total energy consumption in the United 

States in 2013 (U.S. Energy Information Administration, 

2014b). A mix of fuels is used at industrial facilities: natural 

gas and oil products each account for about 40 percent of 

primary energy consumption, renewable sources account for 

about 11 percent, and coal accounts for the remaining 9 percent of consumption. Not all of these fuels are combusted 

to provide energy. Oil and natural-gas products are essential 

ingredients in many petrochemicals, agricultural chemicals, 

and other useful products. The fuel added to these products 

represented about 32 percent of the direct energy resources 

attributed to this sector in 2010 according to a survey by the 

U.S. Energy Information Administration (2010). The remaining 68 percent of the energy resources were used as fuel for 

chemical and mechanical processes, generation of electricity, 

and heating buildings.

Energy-related water needs for the industrial end-use sector are largely unknown. In addition, water is used in industrial 

operations that do not involve energy, such as washing, and it 

may not be possible to distinguish that water use from energyrelated water use. As such, we are not able to provide exact 

details for energy-related water consumption for the industrial 

sector. We can, however, estimate the amount of water that 

would be needed if we ignore the 32 percent of fuels that are 

used as ingredients of other products and assume that the 

remaining 68 percent of energy resources are used to generate 

electricity at the water intensities shown in table 4 for natural 

gas. In this scenario, total annual water consumption for the 

primary consumption of energy is estimated to fall in the range 

of 0.9–4.8 trillion L, and total consumption (which includes 

electricity use) is estimated to fall in the range of 2.0–7.3 trillion L. 

Residential and Commercial

The residential and commercial sectors use energy in 

similar ways. Primary energy consumption for both sectors goes mainly toward heating buildings and secondarily 

toward heating water. Natural gas is the most widely used 

fuel in homes and businesses, accounting for 75 percent of 

direct energy consumption for these sectors. Oil products 

(including natural-gas liquids) and wood account for most of 

the remaining primary energy consumption. The residential 

sector accounted for 7 percent of direct energy consumption 

and almost 38 percent of electricity use in 2013, whereas the 

commercial sector accounted for about 4 percent of direct 

energy consumption and about 36 percent of electricity use 

(U.S. Energy Information Administration, 2014b). 

The energy consumed in generating the electricity for 

the residential and commercial sectors is much greater than 

the primary energy consumed in those sectors. Similarly, total 

energy-related water consumption for these sectors is dominated by the water needed to generate the electricity used in 

these sectors (tables 6 and 7). Water consumption for primary 

energy use is negligible, but water is needed for extracting and 

processing fuels that are used. Total energy-related consumption of water for the residential sector is estimated to be in the 

range of 1.7 to 4.4 trillion L for 2013 (fig. 23), equivalent to 

about 3 to 8 percent of water withdrawn nationwide in 2010 

for public and domestic water supply (Maupin and others, 

2014). Total energy-related water consumption for the commercial sector is estimated to be 1.6 to 3.9 trillion L for 2013 

(fig. 24). 

Primary energy consumption for the residential and 

commercial sectors in 2013 was about 10,000 kWhth on a 

per capita basis; annual water consumption associated with 

the primary energy consumption falls in the range of 600 

to 4,100 L per capita. Total energy consumption for these 

sectors for 2013, including the use of electricity, was about 

36,000 kWhth per capita, and the associated per capita water 

consumption is estimated to be in the range of 10,000 to 

26,000 L. 

Comparison of Water Consumption for Electricity 

and End-Use Sectors

So what do all these water-use numbers tell us? We, as 

Americans, consume a lot of energy. We also consume large 

amounts of water to produce that energy. A summary of 

estimated energy-related water consumption for 2013 is provided in table 8 and figure 25 for individual end-use sectors. 

Estimated total energy-related water consumption is in the 

range of 11.9 to 24.8 trillion L, equivalent to 2 to 5 percent of 

water withdrawn for all uses in 2010. The wide range in these 

estimates illustrates the high level of uncertainty inherent in 

the estimates. The uncertainty makes it impossible to precisely 

quantify water consumption rates.

Figure 22. Estimated water consumption for the production of 

transportation fuels in the United States, 2013.
0

1

2

3

4

Natural gas Oil Biomass Electricity

Water consumption, in trillions of liters

54 The Water-Energy Nexus—An Earth Science Perspective

Table 6. Estimates of energy and related water consumption for primary and total energy consumption for the residential enduse sector in the United States in 2013. Primary consumption is direct consumption of energy. Total consumption includes primary 

consumption and energy consumption required to generate the electricity used in each sector.

[Oil includes natural gas liquids. L, liter; kWhth, kilowatthours of thermal energy; na, not applicable]

Fuel type

Water consumption rate for fuel 

production 

(L/kWhth)

Percent primary 

energy 

consumption for 

sector1

Primary energy 

consumption1

(trillion kWhth)

Percent total 

energy consumption 

for sector

Annual water 

consumed for 

energy use 

(trillion L)

Natural gas 2

0.03–0.4 74 1.48 24 0.0–0.6 

Oil 3

0.4–0.7 14 0.27 4 0.1–0.2

Biomass and other renewables 0 12 0.24 4 0

Primary energy/water use na 100 1.99 32 0.1–0.8

Electricity na na 4.23 68 4

1.6–3.6

Total na na 6.22 100 1.7–4.4

1

U.S. Energy Information Administration (2014a).

2

From table 5.

3

From tables 2 and 5.

4

From table 4.

Table 7. Estimates of energy and related water consumption for primary and total energy consumption for the commercial enduse sector in the United States in 2013. Primary consumption is direct consumption of energy. Total consumption includes primary 

consumption and energy consumption required to generate the electricity used in each sector.

[Oil includes natural gas liquids. L, liter; kWhth, kilowatthours of thermal energy; na, not applicable]

Fuel type

Water consumption rate for fuel 

production 

(L/kWhth)

Percent primary 

energy 

consumption for 

sector1

Primary energy 

consumption1

(trillion kWhth)

Percent total 

energy 

consumption for 

sector

Annual water 

consumed for 

energy use 

(trillion L)

Natural gas 2

0.03–0.4 82 0.98 19 0.0–0.4

Oil 3

0.4–0.7 14 0.17 3 0.1

Biomass and other renewables 0 3 0.04 1 0

Primary energy/water use na 100 1.19 23 0.1–0.5

Electricity na na 4.06 77 4

1.5–3.4 

Total na na 5.25 100 1.6–3.9

1

U.S. Energy Information Administration (2014a).

2

From table 5.

3

From tables 2 and 5.

4

From table 4.

Figure 23. Estimated energyrelated water consumption in 

the residential end-use sector 

of the United States by fuel, 

2013. Oil includes natural-gas 

liquids.
0

1

2

3

4

Natural gas Oil Biomass Electricity

Water consumption, in trillions of liters

0

Transportation Industrial Residential Commercial

Water consumption, in trillions of liters

1

2

3

4

5

6

7

8

9

10

Water in Energy Production and Use 55

Figure 24. Estimated energy-related water consumption in the 

commercial end-use sector of the United States by fuel, 2013. Oil 

includes natural-gas liquids.

Table 8. Estimates of energy and energy-related water consumption in the United States in 2013, by 

end-use sector. Primary consumption is direct consumption of energy. Total consumption includes 

primary consumption and energy consumption required to generate the electricity used in each sector.

[L, liter; kWhth, kilowatthours of thermal energy]

Sector

Primary energy 

consumption1

(trillion kWhth)

Water 

associated with 

primary energy 

consumption 

(trillion L)

Total energy 

consumption1

(trillion kWhth)

Water 

associated with 

total energy 

consumption2

(trillion L)

Transportation 7.90 6.5–9.1 7.92 6.6–9.2

Industrial 6.20 0.9–4.8 9.10 2.0–7.3

Residential 1.99 0.1–0.8 6.22 1.7–4.4

Commercial 1.21 0.1–0.5 5.27 1.6–3.9

Total of end-use sectors 17.30 7.6–15.2 28.51 11.9–24.8

1

U.S. Energy Information Administration (2014a).

2

Water for electricity generation from table 4.

Electricity generation accounts for about 39 percent of all 

energy consumption in the United States. Electricity generation also consumes large volumes of water (table 4). Primary 

energy consumption for electricity generation and the transportation sector consumes similar quantities of water (tables 4 

and 8). Less water is consumed for primary energy consumption in the industrial sector, and much less is consumed for 

primary energy consumption in the residential and commercial 

sectors (table 8). Although there is a large range in estimated 

water consumption rates associated with total energy consumption for each end-use sector, it appears that the transportation sector has the highest energy-related water consumption 

rates followed by the industrial sector and then the residential 

and commercial sectors.

Figure 25. Estimates of 

total energy-related water 

consumption in the United 

States by end-use sector, 2013.

A 110-kilovolt power line.
Fresh groundwater 

and surface water Irrigation

Temporary storage

Water treatment

Thermoelectric plants

Industry

Brackish water

and seawater

Wastewater

treatment Recycle

Commercial

Conveyance

Residential

Distribution

Water Discharge to the environment

source

Collection

Public supply

Thermoelectric

power

Industrial

Livestock

Mining

Aquaculture

Irrigation

Domestic

56 The Water-Energy Nexus—An Earth Science Perspective

Energy for Water Development, Distribution, and Use

About 1.34 trillion L of water were withdrawn daily 

from groundwater and surface-water sources in the United 

States in 2010. The top water-use category was thermoelectric 

power generation, followed by irrigation, public supply, and 

industry (fig. 26). Water may undergo multiple treatment and 

distribution stages before, during, and after its intended end 

use. These stages are collectively referred to as the water-use 

cycle (fig. 27). The typical urban water-use cycle consists of 

the conveyance of water from its source to a point of treatment; treatment and distribution to residential, commercial, 

industrial, and other customers; and collection, treatment, and 

discharge of wastewater back to the environment. Water and 

wastewater treatments are not required for all uses of water. 

Depending on water quality and intended water use, water for 

and wastewater generated from irrigation, power plants, and 

industry may require little or no treatment.

Energy is consumed in each stage of the water-use 

cycle. Depending on the source of water (groundwater or 

surface water) and the distance and topography over which 

it is transported, large amounts of energy may be required to 

move water from its source to treatment plants. The conveyance of surface water by gravity is less energy intensive than 

pumping groundwater, but surface-water conveyances that 

require pumps can be quite energy intensive. In 2010, about 

78 percent of the water used in the United States was supplied 

by surface water, and the rest was supplied by groundwater. 

Energy also is needed to treat and distribute water to end 

users; higher quality water generally requires less energy for 

treatment than poorer quality water. End users consume additional energy by heating and cooling water, circulating it for 

irrigation and other uses, and further treating it by processes 

such as reverse osmosis or ion exchange (water softeners). 

Eventually, water used in homes and businesses must be collected and treated before being returned to the environment or 

recycled, a process that also can use large amounts of energy 

depending on the level of treatment required. 

Water-related energy use represents a substantial part of 

the total energy demand in the United States. A study done by 

the River Network estimated that in 2007 at least 13 percent 

of the Nation’s electricity usage was for heating, moving, and 

treating water (Griffiths-Sattenspiel and Wilson, 2009). In 

California, water-related energy use consumes an estimated 

19 percent of that state’s electricity and 30 percent of its 

natural gas that is not used in power plants (California Energy 

Commission, 2005). Water-related energy usage in the United 

States is likely to increase. The Electric Power Research Institute projected about a 50 percent overall increase in energy 

usage for most freshwater supplies and treatment by the year 

2050 (Electric Power Research Institute, 2002). 

Despite the national importance of energy use for water, 

comprehensive national studies of this topic are lacking. 

According to the U.S. Government Accountability Office, 

comprehensive data about the energy needed for each stage 

of the water-use cycle are limited, and few nationwide studies 

have been conducted on the amount of energy used to provide 

drinking-water and wastewater-treatment services to users 

(U.S. Government Accountability Office, 2011a). In particular, 

Figure 26. Total water withdrawals in the 

United States by category, 2010. (Maupin 

and others, 2014)

Figure 27. A generalized water-use cycle. The 

water-use cycle refers to the overall process of 

(1) collecting, developing, conveying, treating, 

and delivering water to end users; (2) using the 

water; and (3) collecting, treating, and disposing 

of wastewater.
Energy for Water Development, Distribution, and Use 57

energy consumption by water users is difficult to determine 

because electric and gas meters do not differentiate between 

the various uses of the customer. Nevertheless, the available 

data (Griffiths-Sattenspiel and Wilson, 2009; Sanders and 

Webber, 2013) provide a general understanding of the energy 

needs of the water-use cycle. The remainder of this section 

examines the energy requirements of the different stages of the 

water-use cycle—conveyance, treatment, distribution, end use, 

and wastewater collection and treatment. 

Water Conveyance

Water conveyance refers to the withdrawal and transport 

of water from its source (such as an aquifer, river, or lake) 

to the point of treatment or use (fig. 27). The conveyance 

of groundwater generally is more energy intensive (that is, 

it requires more energy per unit volume of water) than the 

conveyance of surface water; pumping is required to withdraw 

groundwater from an aquifer, whereas often gravity can be 

used to move surface water from rivers and lakes to its point 

of use.

Groundwater

About 300 billion L/d of fresh and saline groundwater 

were withdrawn from aquifers in the United States in 2010. 

Groundwater withdrawals vary regionally and seasonally 

depending on intended water use and availability of both 

groundwater and surface water. The amount of energy consumed for groundwater withdrawals also varies. In western 

parts of the United States, most groundwater withdrawals 

occur during the growing season to sustain irrigated agriculture. California withdrew more fresh groundwater in 2010 

than any other state, with about 71 percent of that water used 

for irrigation (Maupin and others, 2014). The electrical energy 

used to pump groundwater for irrigation in California in 2001 

represented about 10 percent of all the water-related energy 

use in the state (California Energy Commission, 2005). In 

eastern parts of the United States, however, a larger percentage 

of groundwater withdrawals is for public supply, which means 

that withdrawals and associated energy consumption occur 

somewhat uniformly throughout the year. Florida had the sixth 

largest statewide fresh groundwater withdrawals in the Nation 

in 2010, with most of that water used for public supply.

The energy intensity of groundwater pumping depends 

on pumping depth and the efficiency of the pump. About 3.5 

to 7 kWh of electricity are required to lift 1 million L of water 

1 m, depending on pumping efficiency, so the deeper the 

groundwater, the more energy is required to bring that water 

to land surface. Public-supply wells consume an estimated 

average of 159 kWh per million liters (ML) of pumped 

groundwater (Electric Power Research Institute, 2002). 

Energy intensities for groundwater pumping from different 

depths in California were estimated to be in the range of 143 

to 608 kWh/ML (Cohen and others, 2004). Declining water 

levels in aquifers, whether from over pumping or drought, 

generally result in rising energy costs for pumping. The two 

most heavily pumped aquifer systems in the United States, 

the High Plains aquifer in the west-central United States and 

the Central Valley aquifer system in California, have already 

experienced large water-level declines. To some extent, 

the increased energy costs associated with pumping deeper 

groundwater could be offset by using more efficient equipment. High-efficiency groundwater pumps are more expensive than standard pumps, but they use 10 to 30 percent less 

energy; the extra cost typically is recovered quickly through 

energy savings and lower maintenance costs (Electric Power 

Research Institute, 2009).

Pumping groundwater from aquifers for water supply (left) is much more energy intensive than moving surface water by gravityfed pipelines and canals (right).
58 The Water-Energy Nexus—An Earth Science Perspective

The volume of groundwater withdrawals and associated 

energy use at any location could vary as a result of changes in 

climate. Drought, for example, could lead to increased energy 

use by necessitating more overall groundwater pumping, both 

for agricultural uses and to offset reductions in surface-water 

supplies used for drinking water or for cooling at thermoelectric power plants, which could in turn lower water levels in 

aquifers. In the Central Valley of California, the volume of 

groundwater pumped for agriculture during a typical dry year 

was more than twice the volume pumped during a typical wet 

year (Faunt, 2009). Managed aquifer recharge is a watermanagement option that can help address problems at areas 

that experience periodic water stresses (see Box L—Managed 

Aquifer Recharge of Recoverable Water).

Surface Water

In 2010, about 1.04 trillion L of fresh and saline surface 

water were withdrawn daily from rivers, lakes, and other water 

bodies in the United States, more than three times the volume 

of groundwater withdrawals. Surface-water withdrawals vary 

by region and season across the Nation for some of the same 

reasons that groundwater withdrawals vary. California had the 

largest volume of state-wide fresh surface-water withdrawals 

in the Nation in 2010, with approximately 77 percent of that 

water used for irrigation during the growing season. In other 

western States, such as Colorado, upwards of 90 percent of 

the fresh surface-water withdrawals are used for irrigation. In 

eastern parts of the United States, a much larger percentage of 

withdrawn surface water is used for cooling at thermoelectric 

power plants, a process that requires year-round withdrawals. Illinois, for example, had the fourth largest volume of 

fresh surface-water withdrawals in the Nation in 2010, with 

about 88 percent of that water used for cooling (Maupin and 

others, 2014).

Despite the large volume of surface-water withdrawals, the energy intensity of this activity can be quite low for 

gravity-fed conveyances. Gravity-fed conveyances provide 

surface water to some of the largest metropolitan areas and 

agricultural regions of the Nation. The drinking-water supply 

for New York City, for example, consists in part of a network 

of reservoirs located as far as 200 km from the city, yet 95 percent of the conveyance is gravity fed. Another gravity-fed 

conveyance, the roughly 130-km-long All-American Canal, is 

one of the largest irrigation canals in the world and transports 

water from the Colorado River near Yuma, Arizona, to irrigated cropland in the Imperial Valley in southeastern California (Loeltz and Leake, 1979). 

Not all surface-water conveyances, however, can be fed 

by gravity. Delivery of water from northern to southern California by the State Water Project, for example, requires pumping the water nearly 600 m up and over the Tehachapi Mountains at the Edmonston Pumping Plant. In 2000, the energy 

intensity of that operation was about 1,850 kWh/ML, more 

than 10 times the previously cited average energy intensity for 

groundwater pumping at municipal supply wells (California 

Department of Water Resources, 2002). Thus, topography is 

an important control on the energy intensity of surface-water 

conveyances.

The energy intensity of water conveyance also is dependent on the efficiency of the infrastructure. Leaks from unlined 

canals can be substantial, as can evaporation from the open 

water surfaces of large reservoirs. The energy costs associated 

with leaks and evaporation are greater for canals, pipelines, 

and reservoirs filled with water by pumping than they would 

for those that are gravity fed because of the increased cost of 

pumping water for a prescribed amount of delivered water. 

The potential for leakage and evaporation generally increase 

as the distance of water transport in canals and pipelines and 

the water residence time in reservoirs increase. The annual 

evaporative loss from Lake Mead, about 720 trillion L (Moreo 

and Swancar, 2013), is equivalent to about 2 percent of the 

average volume of the reservoir. Conveyances to Lake Mead 

are gravity fed, so leaks and evaporation do not add substantially to the amount of energy required to deliver water to the 

lake. The evaporation from Lake Mead can be viewed as a lost 

source of energy generation, however, because the water that 

evaporates does not pass through the Hoover Dam hydroelectric turbines. In some instances, it is economically feasible to 

stop or reduce the loss of water from surface-water bodies. 

At the Edmonston Pumping Plant, water 

is pumped up nearly 600 m as part of the 

California State Water Project.

Continued on page 60
Energy for Water Development, Distribution, and Use 59

Managed Aquifer Recharge of Recoverable Water

The ability to store water in times of plentiful 

precipitation and recover water in times of scarcity is highly desirable for a number of reasons. 

Interest in storage and recovery systems is likely to 

expand because of growing human populations and the risk 

of increased climate variability. In the past, this watermanagement objective was often met by constructing dams 

to impound surface water. Few large dams have been constructed in the United States since the middle of the 20th 

century. Increasingly, managed aquifer recharge is being 

used to store and recover water for later use. In addition to 

economic and environmental benefits, underground storage 

systems avoid the large water losses that occur in surface 

reservoirs as the result of evaporation.

Managed aquifer recharge (MAR) is the purposeful 

recharge of water into an aquifer. The intent of the operation is usually to store water for future recovery and use; 

however, MAR is also used to inhibit saltwater intrusion 

and land subsidence. Surface water, groundwater, treated 

wastewater, and other recycled water have all been used 

to recharge aquifers in MAR systems. The chosen type of 

recharge water and level of pre-injection treatment depend 

in part on the intended use of the water, the availability of 

water sources, and the water’s chemical compatibility with 

aquifer solids and native groundwater. Depending on site 

conditions, the host aquifer is recharged through constructed recharge basins, direct recharge wells, or shallow 

wells completed above the water table. Water can be recovered by extraction wells that pump water out of the aquifer. 

The recovered water might or might not undergo treatment prior to use, depending on the extent of the chemical 

alteration of the water while in storage in the aquifer and 

the intended use of the water. In some MAR systems, the 

chemical quality of stored water actually improved during 

its residence time in the aquifer (National Research Council, 2008b). 

Managed aquifer recharge systems are located 

throughout the United States and the number of systems is 

growing rapidly (Pyne, 2005; National Research Council, 

2008b). Most of the systems are located in coastal areas 

and arid regions of the southwestern United States, but 

some MAR systems also are located in humid, interior 

regions of the country. Most MAR systems are used for 

municipal water supply, but others are used for irrigation and cooling supplies and to control saltwater intrusion. Managed recharge is done at many different scales. 

In Orange County, California, managed recharge offsets 

pumping demands on the groundwater basin that provides 

over half the water needs for 2.4 million people (Orange 

County Water District, 2014). The advanced treatment 

and recharge process uses less than half the energy that 

it takes to transport an equivalent amount of water from 

northern California and less than one third of the energy 

required to desalinate that much water. On a smaller scale, 

the City of Tigard, Oregon, with a population of 48,695 in 

2012, injects water into a local aquifer during the winter 

months and pumps it back out for use in the summer (City 

of Tigard, 2014). The energy intensity of MAR systems 

has not been examined in detail but should be similar to 

that of groundwater with some additional energy required 

for conveyance of water to and from the recharge site. As 

demand for water increases, MAR systems could be a more 

energy-efficient option than alternatives such as conveying 

water over long distances or treating saline water.

Sand Hollow Reservoir, constructed for managed aquifer recharge in 

southwestern Utah, has become a popular destination for boating and fishing.
Raw waterRaw water

Home

consumption Finished

water storage

Disinfectant

basin Filter

Coagulants

Corrosion

control Disinfectant Fluoride

Polymer Coagulation/

flocculation basin Sedimentation basin

60 The Water-Energy Nexus—An Earth Science Perspective

The Coachella Canal lining project in southern California 

replaced 56 km of unlined canal with concrete-lined canal 

and in the process saved about 90 million L/d of water that 

otherwise would have been lost to seepage (San Diego County 

Water Authority, 2013). Much of the conserved water provides 

a new water supply for San Diego County; it is worth noting, 

however, that some of the water that was lost to canal seepage 

prior to the project actually helped to replenish local groundwater supplies in the vicinity of the canal.

Water Treatment

Water for commercial, industrial, and residential purposes usually requires treatment prior to or during use 

(fig. 27). The energy intensity of water treatment depends on 

the water source, quality of the source water, the intended 

use of the water (not all uses require treatment to drinkingwater standards), and the chosen treatment process. The 

age of water-treatment infrastructure also could affect overall energy intensity because old infrastructure may be less 

energy efficient or could leak more than new infrastructure. 

With respect to freshwater, the treatment of groundwater to 

drinking-water standards commonly is less energy intensive than the treatment of surface water. Groundwater often 

only requires disinfection, such as by chlorination, whereas 

surface-water treatment is a multistage process that usually 

includes not just disinfection but also processes like flocculation, sedimentation, and filtration to coagulate and remove 

sediment and other particles (table 9 and fig. 28). The energy 

intensity of groundwater chlorination is estimated to be less 

than 2.6 kWh/ML, whereas the energy intensity of multistage 

surface-water treatment is estimated to be about 26 kWh/ML, 

or more than a 10-fold increase over the energy intensity of 

groundwater treatment (Electric Power Research Institute, 

2002). Neither of these estimates includes the energy required 

to distribute treated water to end users, which can have a much 

higher energy intensity than the water-treatment process itself; 

distribution is discussed in a subsequent section. While energy 

sources other than electricity are occasionally used for water 

treatment, 93 percent of water providers receive 90 percent 

or more of their operating energy from electricity (GriffithsSattenspiel and Wilson, 2009).

These estimates for the energy intensity of water treatment assume a freshwater source, yet increasing interest is 

being given to saline groundwater and seawater as drinkingwater sources in areas that lack adequate supplies of freshwater. Total desalination capacity in the United States in 2005 

was about 57,000 million L/d, or about 3 percent of the total 

water withdrawals for public supply (National Research Council, 2008a). Two-thirds of that desalination capacity is used for 

municipal water supply. The states with the largest installed 

desalination capacity are Florida, California, and Texas, all 

coastal states with large populations, and Arizona, an arid 

state. Desalination of groundwater and seawater to drinkingwater standards requires a substantial amount of energy. In 

California, the energy intensity for treatment of saline groundwater is about 1,060 to 2,600 kWh/ML; treatment of estuarine 

water and seawater requires an intensity of about 2,600 to 

4,000 kWh/ML. These energy intensities represent increases 

of as much as 1,500 and 150 times the intensities for treating 

fresh groundwater and surface water, respectively. When the 

Table 9. Percentage of community water-treatment plants using different treatment schemes.

[Data from U.S. Environmental Protection Agency (2002). Values are percentages]

Treatment practice Groundwater plants Surface-water plants

Disinfection only 55 11

Disinfection and other treatment 45 89

Figure 28. Schematic 

representation of the process 

used by the Denver Water 

public agency to treat surface 

water. (Denver Water, 2014)
Energy intensity, in kilowatthours per million liters

Wastewater

reuse

Groundwater Brackish

water

Deep

groundwater

Surface Seawater

water

(gravity)

0

1,000

2,000

3,000

4,000

Energy for Water Development, Distribution, and Use 61

energy intensities for conveyance and treatment are combined, however, the differences in intensity between the water 

sources can be much less (fig. 29). 

The energy intensity of water treatment is likely to 

decrease as more efficient technologies are adopted. New 

technologies related to pump design and pipeline optimization 

could save 5 to 30 percent of the energy associated with those 

components of a treatment plant, potentially saving the cost 

of millions of kilowatthours of electricity each year (table 10). 

Advanced treatment technologies associated with disinfection, 

such as ozone and ultraviolet-light treatments, could save 10 

to 30 percent of the energy associated with chlorination. These 

new treatments are important because the use of chlorine to 

disinfect water has come under scrutiny as it could generate 

Figure 29. Typical energy intensities associated with the conveyance and treatment of water, by 

source. (Modified from Electrical Power Research Institute, 2009)

Table 10. Estimated energy savings for selected water technologies.

[Data from Electric Power Research Institute (2009). %, percent; kWh/yr, kilowatthours per year]

Technology Percent savings potential

Potential electrical energy savings 

in public water supplies 

(million kWh/yr)

High-efficiency pump/motor systems 10 to 30% of pumping energy 2,600–7,800

Pipeline optimization 5 to 20% of pumping energy 1,300–5,200

Advanced membranes 15 to 25% of treatment energy 117–195

Advanced ozone 10 to 20% of treatment energy 572–654

Advanced ultraviolet 10 to 30% of treatment energy 515–544

Advanced reverse osmosis 50% of desalination treatment energy 2,400

Capacitive deionization 50% of brackish water treatment energy 1,000

Membrane distillation 66% of desalination treatment energy 3,200

disinfection byproducts such as chloroform that potentially 

can be harmful to human health (Rostad, 2007). Advanced 

treatment technologies related to reverse osmosis and membrane distillation could save even more energy (50 percent or 

more) when used for desalination. 

Regulatory standards also affect the energy intensity of 

water treatment. The Safe Drinking Water Act governs what 

concentrations of selected chemical, radioactive, and biological constituents are safe in public drinking water. More 

restrictive standards (that is, lower limits on concentrations of 

some constituents) generally require more energy-intensive 

treatment methods. As an example, arsenic concentrations 

in drinking water have long been a concern. In 2002, the 

U.S. Environmental Protection Agency finalized a reduction in 
62 The Water-Energy Nexus—An Earth Science Perspective

the arsenic standard from 50 to 10 micrograms per liter (μg/L). 

That standard went into effect in 2006. The energy costs associated with upgrading water-treatment facilities to meet the 

lower arsenic standard were a particularly relevant issue for 

suppliers of groundwater because groundwater tends to have 

higher arsenic concentrations than surface water. A study of 

the quality of water from public-supply wells found that about 

10 percent of the source-water samples (groundwater collected 

before the point of treatment) had arsenic concentrations that 

exceeded the new 10-μg/L standard (Toccalino and Hopple, 

2010). Less than 1 percent of the samples exceeded the old 

standard (50 μg/L), so lowering the standard meant that more 

wells would be out of compliance unless some type of action 

was taken. Several processes are available for removing arsenic from water, such as an activated alumina treatment, which 

can require up to 26 kWh/ML (U.S. Environmental Protection 

Agency, 2003), a substantial increase in energy requirements 

for those facilities that were required to upgrade their treatment process to meet the reduced arsenic standard.

Water Distribution

Distributing treated water to end users requires more 

energy than the water treatment process itself. The Electric 

Power Research Institute estimated an energy intensity of 

about 317 kWh/ML for distributing drinking water from 

surface-water treatment plants with a capacity of at least 

3.8 million L/d (Electric Power Research Institute, 2002), 

whereas the energy intensity of the treatment process is about 

26 kWh/ML. For groundwater, the estimated intensity for distribution was also about 317 kWh/ML, but the energy intensity 

of treatment by chlorination is about 2.6 kWh/ML. The energy 

intensity of water distribution depends to a large extent on the 

distance and elevation of the treatment plant in relation to end 

users. As indicated previously, about 3.5 to 7 kWh are required 

to lift 1 million L of water 1 m; pumping water requires 

energy.

The efficiency of water delivery systems also affects the 

associated energy requirements. As discussed in the section 

“Water Conveyance,” pipelines have the potential to develop 

leaks. As water loss from a delivery system increases, the 

amount of energy required to provide the prescribed amount 

of water received at the destination increases. The potential for 

water leakage often increases with the age of the distribution 

system. Water utilities are continually upgrading distribution systems, but the task is very large and inevitably there 

will be old water mains in some distribution systems. In its 

2000 Community Water System Survey, the U.S. Environmental Protection Agency estimated that community water 

systems maintain more than 3 million km of distribution 

mains. Seventy-eight percent of those mains were less than 

40 years old, 18 percent were 40 to 80 years old, and 4 percent 

were more than 80 years old (U.S. Environmental Protection 

Agency, 2002). The efficiency of the delivery of treated water 

is of particular concern because of the relatively high energy 

cost for treatment and delivery. Loss from water mains during delivery are commonly in the range of 10 to 60 percent 

(Passarello and others, 2012), implying that if all leaks were 

repaired, then water and related energy use could be reduced 

by more than one half. A mere 5 percent reduction in water 

distribution system leakage in the United States could save 

about 1 billion L/d of water and 313 million kWh of electricity 

annually (Griffiths-Sattenspiel and Wilson, 2009).

End Use

Once water arrives at a residence or place of business, 

it may undergo additional processing for heating, further 

purification, or pressurization. All of these processes consume 

energy. The hot showers and baths we enjoy, in particular, 

consume substantial amounts of energy. The energy intensity 

of heating water for bathing or dishwashing is about 42,000 

to 54,000 kWh/ML (table 11), which is about 10 times higher 

than that for desalination of seawater (fig. 29). In fact, water 

The City of San Diego, California, installed a 1.5 million kWh/yr 

solar photovoltaic energy system at its Otay Water Treatment 

Plant. The solar system has the capacity to provide enough 

energy to power the plant’s treatment of about 130 million L 

of water each day, thereby avoiding the release of more than 

0.454 million kg of carbon dioxide to the atmosphere each year 

(U.S. Department of Energy, 2010).
Energy for Water Development, Distribution, and Use 63

The Energy Intensity of Bottled Water

Bottled water is a popular beverage in the 

United States. In 2011, consumers purchased more 

than 34 billion L of bottled water. Energy is required 

to produce, treat, package, and transport that water to 

consumers. Energy also is required to make the plastic bottles that contain the water. Gleick and Cooley (2009) examined the energy intensity of bottled water and determined 

that delivering bottled water to the end user requires up to 

2,000 times more energy than delivering tap water (which 

includes the typical energy costs of conveyance, treatment, 

and distribution of tap water). The two components of bottled-water delivery that require the most energy are transportation of the water from the bottling plant to the point 

of sale and manufacture of the plastic bottles (table M–1). 

Some brands of bottled water have water sources in the 

United States, but others are sourced in Europe, the South 

Pacific region, and other distant locations. According to the 

analysis by Gleick and Cooley (2009), the energy costs of 

transporting bottled water from Europe or the South Pacific 

to markets in the United States are about 3 to 4 times 

greater than the energy costs for transportation from local 

sources in the United States. Although the energy intensity 

associated with bottled water is large, the actual volume of 

water that is consumed is small when compared to the volume of tap water consumed—the volume of bottled water 

consumed in the United States in a year would only supply 

our national tap water needs for about 5 hours, on the basis 

of 2011 bottled-water sales and groundwater and surfacewater withdrawals for public and domestic supplies in the 

United States in 2010.

Table M–1. Energy requirements for producing bottled water. 

[Data from Gleick and Cooley (2009). kWhth/L, kilowatthour of thermal 

energy per liter of water]

Stage of production Energy intensity 

(kWhth/L)

Manufacture of plastic bottle 1.1

Treatment at bottling plant 2.8×10-5–0.006

Filling, labeling, and sealing of bottle 0.003

Transportation: 3 scenarios 0.39–1.6

Cooling 0.06–0.11

Total 1.6–2.8

Typical energy intensity of tap water 0.001

Approximately 40 billion L 

of bottled water were 

consumed in the United 

States in 2013.

heating is the most energy-intensive process in the water-use 

cycle. Residential and commercial hot-water heaters account 

for about 79 percent of all energy used in the water-use cycle 

for those sectors, far exceeding the combined energy consumption associated with the conveyance, treatment, and 

delivery of water to the end user (Griffiths-Sattenspiel and 

Wilson, 2009). More cold water, mostly for flushing toilets 

and landscape irrigation, is used at residences than hot water, 

but cold-water use has a relatively low energy intensity. Similarly, other end-use processes, such as pressurization or water 

purification, consume very little energy relative to the energy 

that is used to heat water. 

Agricultural water generally is less energy intensive 

than urban water. Nevertheless, saving water by using more 

efficient irrigation techniques or by growing crops that use 

less water could save energy associated with the conveyance 

of water to fields. Surface flood irrigation of cropland has an 

average irrigation efficiency (the percent of applied water that 

is actually taken up by the crop) of only 50 percent, whereas 

average efficiencies for center-pivot sprinklers and subsurface 

drip irrigation systems are 85 and 90 percent, respectively 

(Electric Power Research Institute, 2009). Much of the water 

applied to fields using flood irrigation percolates below the 

root zone and is not used by the crop.

As with other of components of the water-use cycle, 

efficiencies gained through technological upgrades in equipment and minimization of system leaks result in direct energy 

and water savings for end users. Of the various water-cycle 

components, however, end use is unique in that water conservation by end users also results in energy and water savings at 

the early stages of the water-use cycle (conveyance, treatment, 

and distribution) and at the late stages (wastewater collection 

and treatment). An added benefit of water conservation is that 
64 The Water-Energy Nexus—An Earth Science Perspective

more water could remain in aquifers, streams, lakes, and other 

water bodies for environmental uses.

In urban areas, replacing the old equipment that moves or 

uses water, such as plumbing and toilets, with more efficient 

models would result in substantial energy and water savings 

(table 12). The California Energy Commission estimated that 

the installation of ultra low-flow toilets in residences within 

the state would result in a savings of about 3 billion kWh of 

electricity over 25 years (table 12). The use of recycled water 

could save further energy and water by reducing the demand 

for new, more energy-intensive water supplies (see Box N—

Recycled Water in California).

Residential and commercial hot-water heaters used for hot tubs, 

dishwashers, baths, and showers account for about 79 percent 

of all water-related energy consumption for those sectors. The 

U.S. Department of Energy offers a number of tips for reducing energy 

consumption associated with hot-water heaters; these include using 

less hot water, turning down the water heater’s thermostat, installing 

low-flow faucets and showerheads, and installing a more energyefficient heater, such as an on-demand tankless heater or a heater 

that is powered by solar or geothermal energy. (U.S. Department of 

Energy, 2013c)

Table 11. Estimated energy intensity of heating water for 

selected residential water uses.

[Values are in kilowatthours per million liters of water]

Water-use category Energy intensity1

Dishwasher 53,800

Bath 42,000

Shower 39,300

Faucet 39,100

Clothes washers 15,000

Leaks 14,400

Toilet 0

Landscape irrigation 0

1

Based on data from Griffiths-Sattenspiel and Wilson (2009) and 

DeOreo and Mayer (2001).

Table 12. Energy value of water saved as the result of the implementation of selected water-efficiency measures in California, 2004.

[Data from California Energy Commission (2005). ML, million liters; kWh, kilowatthours; na, not applicable]

Efficiency measure Annual savings Useful life 

(years)

Life-cycle electricity savings 

Water (ML) Electricity (kWh) (kWh)

Residential plumbing retrofit 1,180 2,814,000 5 14,070,000

Metering 6,000 14,317,200 11 157,489,200

High-efficiency washing machine rebate 1,200 2,860,100 15 42,901,500

Residential ultra low-flow toilets 49,000 117,184,600 25 2,929,615,000

Large landscape conservation programs 20,100 34,595,450 10 345,954,500

Commercial, institutional, and industrial 

ultra low-flow toilets

980 2,328,300 25 58,207,500

Commercial, institutional, and industrial 

conservation programs

18,200 43,433,300 12 521,199,600

Statewide totals 96,660 171,771,350 na 4,069,437,300
Headworks

Waste-activated

sludge

Air Bisulfate

Polymer Air

Chemical

sludge

Primary

sludge

Grit and

screenings

Dechlorination

Filters

Primary

clarifiers

Chemical

clarifiers

Chlorine

contact

Cl2

Alum

(optional) Lime Alum Biological

nutrient

removers

Energy for Water Development, Distribution, and Use 65

Wastewater Collection

Wastewater collection refers to the transfer of wastewater 

from its point of generation in homes, businesses, and elsewhere to a wastewater treatment plant. The energy intensity of 

wastewater collection on average is about 40 kWh/ML (California Energy Commission, 2005), which is relatively small 

compared to the energy intensity of water distribution (about 

317 kWh/ML). Wastewater treatment plant operators generally try to place their facilities at a lower elevation than that 

of their customers to take advantage of gravity and thereby 

minimize pumping. Leakage rates from wastewater collection 

networks, or sewers, are generally considered to be less than 

those from water mains because these systems are not pressurized. Leakage rates for wastewater networks are typically 

in the range of 5 to 20 percent (Schirmer and others, 2013), 

but rates as high as 56 percent have been reported (Rutsch and 

others, 2008). Leakage from sewer lines could affect the quality of the receiving groundwater and surface water (Lerner, 

2002; Schirmer and others, 2013) and potentially the treatment 

costs for downstream water users.

An additional concern is that low pressures within sewer 

systems can allow groundwater to seep into leaky pipes, thus 

adding to the amount of water that must be treated and the 

amount of energy consumed at wastewater treatment facilities 

(Wittenberg and Aksoy, 2010). Groundwater seepage can be 

particularly problematic during intense precipitation events, 

when it is not uncommon for stormwater to enter sewer 

systems. There is no way to differentiate between stormwater 

and sewage once it enters a sewer system, so both are processed at the wastewater treatment plant. Because the energy 

used to treat wastewater is proportional to the influent flow 

rate, increased flows caused by stormwater result in increased 

energy use by the plant. Excessively large stormwater inflows 

to wastewater treatment plants can potentially exceed the 

treatment capacity of the plants, resulting in the release of 

untreated wastewater into the environment.

Wastewater Treatment

Approximately 40,000 publicly or privately owned 

wastewater treatment plants operate in the United States (Solley and others, 1998). These plants are designed to remove 

physical, biological, and chemical contaminants from wastewaters received from residential, commercial, and industrial 

sources (as described in the previous section, treatment 

plants sometimes receive storm runoff as well). A number 

of techniques may be used for treating wastewater, most of 

which require energy. New processes are continually being 

developed in attempts to reduce energy requirements; in fact, 

recently developed techniques can capture and use energy 

contained in wastewater.

Multiple processes are applied at most municipal 

wastewater treatment plants, including screening out debris, 

removing suspended solids and grease, removing nutrients, 

chlorination, filtering, and dechlorinization (fig. 30). During 

these processes, solids are separated from the water, oxygen is 

added to promote biologic activity, water is disinfected with 

chlorine or ultraviolet light, and nutrients and other chemicals 

are filtered out. 

The amount of energy needed to treat wastewater 

depends on the plant size and the specific treatment methods 

that are applied. Energy use for public and private wastewater treatment plants was 74 billion kWh in 2005, or about 

15 percent of the energy used in the entire water-use cycle for 

the residential and commercial sectors (Griffith-Sattenspiel 

and Wilson, 2009). Energy intensity generally decreases with 

increasing plant size because of economies of scale, but the 

intensity increases with increasing level of treatment (Electric 

Power Research Institute, 2002). The most energy-intensive 

process is the treatment of the extracted solid materials, often 

referred to as sludge or biosolids. The solids are collected 

into sludge digesters where anaerobic reactions and heat are 

used to degrade biological contaminants. Sludge digesters can 

consume 30 to 80 percent of all electricity used at wastewater 

treatment plants (Center for Sustainable Systems, 2013). 

Figure 30. Summertime treatment processes at Clean Water Services’ wastewater treatment facility in Durham, Oregon. (Diagram 

reproduced with permission from Clean Water Services)

Continued on page 67
Agricultural

irrigation

(46 percent)

All

other uses

(19 percent)

Groundwater

recharge

(14 percent)

Landscape

irrigation

21 percent

City City

Water treatment

plant

Wastewater

treatment plant

Farm

Well

Disinfection

Factory

Recharge basin

Groundwater

Stream

Effluent Influent

River

Co-mingled effluent

and natural runoff

1. Direct industrial reuse

2. Instream flow augmentation

3. Direct agricultural reuse

4. Groundwater recharge

1

2

5

3

6

7

8

4

5. Urban reuse (landscape, toilet flushing,...)

6. Indirect potable reuse from river

7. Indirect potable reuse from well

8. Indirect agricultural reuse

66 The Water-Energy Nexus—An Earth Science Perspective

Recycled Water in California

The California Sustainability Alliance defines 

recycled water as municipal, industrial, or agricultural 

wastewater, which, as a result of treatment, is suitable 

for a direct beneficial use or a controlled use that would 

not otherwise occur. Recycled water represents the fastest growing new source of water in California (California 

Energy Commission, 2005). This trend is related to the large 

volume of treated wastewater that is potentially available 

for reuse and the fact that the energy intensity of recycled 

water is small relative to that of other water sources. 

California water agencies used about 0.6 trillion L 

of recycled water in 2001; by 2030, usage is estimated 

to be 2.2–2.7 trillion L (California Department of Water 

Resources, 2009). The primary uses were for agriculture 

irrigation, landscape irrigation, and groundwater recharge 

projects (fig. N–1). In general, the uses of recycled water 

are broadly grouped into direct and indirect uses (fig. N–2). 

Direct uses are those intentional uses such as irrigation 

and groundwater recharge that use water directly from the 

wastewater treatment plant (fig. N–2). Indirect uses are those 

unintentional or intentional uses of treated wastewater that has 

spent time in an aquifer or surface-water body such as a stream 

or wetland. In reality, indirect use of treated wastewater has 

occurred for many years across the United States where treated 

wastewater is discharged to rivers and septic-tank effluent 

recharges aquifers and where downstream users withdraw that 

water for new purposes. 

Recycled wastewater is energy efficient because conveyance from a source is not required and wastewater has to 

undergo some level of treatment anyway. Some energy might 

be required for extra treatment, depending on the intended 

use, and for distribution to the end user. Wastewater that has 

Figure N–1. The State of California’s use of 

recycled wastewater, 2001, as a percentage of the 

total amount of about 0.6 trillion liters. Most of the 

recycled wastewater was used for agricultural and 

landscape irrigation and for groundwater recharge 

projects. (Data from the California Department of 

Water Resources, 2009)

Figure N–2. Schematic illustration of some possible 

direct and indirect uses of recycled wastewater. (Used with 

permission of the California Division of Water Resources)
0

1,000

3,000

4,000

5,000

6,000

Energy intensity, in kilowatthours per million liters

1 2 3 4 5

Distribution

Treatment

Conveyance

EXPLANATION

(1) Recycled water (San Diego, tertiary treatment)

(2) Recycled water (San Diego, secondary treatment)

(3) Colorado River water (San Diego)

(4) State Water Project water (San Diego)

(5) Seawater desalination water (Carlsbad estimated)

2,000

Aerial view of the Carson, California, West Basin water 

recycling facility.

Energy for Water Development, Distribution, and Use 67

The Clean Water Act governs the discharge of 

pollutants into the waters of the United States. As with 

the Safe Drinking Water Act, new regulatory standards could alter the energy intensity of treatment in 

the future. Of particular concern are chemicals that the 

U.S. Environmental Protection Agency refers to as contaminants of emerging concern (CECs) (U.S. Environmental Protection Agency, 2014b). These are chemicals 

that have only recently been detected in surface water 

and groundwaters and whose risk to human health 

and the environment are unknown. Included in this 

group are pharmaceuticals, personal care products, and 

perfluorinated compounds. Studies have found that the 

level of removal of those chemicals from wastewater 

is dependent on factors such as the type of chemical 

compound and the treatment process. One study examined the treatment efficiency for removing 55 CECs 

from wastewater streams; on average, standard treatment processes removed over 85 percent of the CECs 

(Kasprzyk-Hordern and others, 2009). If more restrictive 

regulatory standards are put in place for CECs, then 

more energy-intensive, enhanced treatments will likely 

need to be implemented to meet those standards. This 

example reinforces the message that protecting water 

quality saves energy.

Organic matter contained in wastewater can be 

an important and useful source of energy. According 

to the Water Environment Research Foundation, the 

energy content of wastewater and biosolids exceeds the 

energy needed to treat that wastewater by a factor of 10 

(Water Environment Research Foundation, 2011). As of 

2011, 104 wastewater treatments plants with anaerobic 

digesters in the United States were using the microbial 

methane produced in their digesters to generate electricity and heat; the combined capacity of these plants 

is 190 MW (U.S. Environmental Protection Agency, 

2011a). This power-generating process could be carried 

out economically at hundreds of additional treatment 

plants. Development of “high performance” microorganisms that anaerobically digest waste more efficiently 

could increase the methane yield at wastewater treatment plants. Recent studies indicate that fully anaerobic 

treatment processes could generate substantially more 

methane than conventional aerobic/anaerobic treatment 

processes, possibly to the point of making wastewater 

treatment a net producer of energy (McCarty and others, 

2011). Capturing the methane generated in treatment 

has the added benefit of eliminating direct release of 

that greenhouse gas into the atmosphere. Fully anaerobic wastewater treatment offers increased potential for 

achieving energy and cost savings, but more work needs 

to be done before this technology is adopted by the 

wastewater industry. 

Figure N–3. Relative energy intensity of selected water 

sources in southern California. (Modified from California 

Sustainability Alliance, 2008)

undergone tertiary treatment is acceptable for a broader 

group of uses than wastewater that has undergone only secondary treatment. If wastewater treated to a secondary level 

was intended for a more restricted use such as the irrigation 

of food crops, then additional energy would be required to 

treat the water to a higher level before it was used. Despite 

the additional energy that might be needed to use treated 

wastewater, it is still a less energy-intensive source of water 

than many others in California (fig. N–3).
Water-cycle component (annual energy use,

billion kilowatt-hours equivalent)

EXPLANATION

1.2 percent 3.9 percent

15.4 percent

16.4 percent 63.1 percent

Residential water heating (304)

Commercial water heating (79)

Wastewater treatment (74) 

Residential supply (19)

Commercial supply (5.9)

End uses

Conveyance,

treatment and

distribution

68 The Water-Energy Nexus—An Earth Science Perspective

Septic systems are onsite wastewater treatment systems 

commonly used at homes whose plumbing is not connected 

to a centralized wastewater treatment plant. According to the 

2010 U.S. Census, about 19 percent of the estimated 115 million occupied homes in the United States used some type of 

onsite wastewater treatment system (U.S. Census Bureau, 

2014). The treatment processes and equipment used in septic 

systems are quite simple in comparison with most centralized wastewater treatment plants, so septic systems typically 

have very low energy intensities. When properly designed, 

constructed, and maintained, septic systems can provide 

good treatment of wastewater, but septic systems that are not 

operating properly have the potential to degrade groundwater 

and surface-water quality (Katz and others, 2011), which 

ultimately could lead to higher energy costs associated with 

treatment for downstream water users. 

Summary of Water-Related Energy Use

Energy consumed in providing and treating water represents an important part of the Nation’s energy demand. As 

discussed in the preceding sections, energy is required for 

transporting water and for treating it before, during, and after 

use. The actual amount of energy required for all stages of the 

water-use cycle varies greatly across the country depending 

on location of water source and use, quality of water, intended 

use, and technologies that are employed. Total water-related 

energy consumption in the United States in 2005 for residential and commercial uses is estimated to be equivalent to about 

482 billion kWh of electricity (fig. 31), or about 15 percent of 

all the electricity used in the United States. Details on industrial water-related energy use are lacking because much of that 

information is proprietary and unavailable to the public (Sanders and Webber, 2012), and water-related energy consumption 

for the transportation sector is assumed to be negligible. The 

most energy-intensive treatment stage of the water-use cycle 

for the residential and commercial sectors is heating water; 

hot-water heaters account for about 79 percent of waterrelated energy consumption. Reducing the use of hot water 

and improving techniques for heating water might be the most 

effective ways for reducing water-related energy consumption 

in the United States. 

Figure 31. Annual water-related energy use in the residential 

and commercial sectors of the United States, 2005. Energy use in 

kilowatthours of equivalent electricity takes into account the fact 

that about 50 percent of the energy used for heating water comes 

from natural gas. (Griffiths-Sattenspiel and Wilson, 2009)

Demonstration wetland at Henderson, Nevada, where vegetated 

hummocks were built into the wastewater treatment wetland to 

improve its effectiveness and sustainability, as well as provide 

quality wildlife habitat.
Science for Addressing the Water-Energy Nexus 69

Science for Addressing the Water-Energy Nexus

Establishing sustainable supplies of freshwater and 

energy for future generations are goals that have widespread 

support within the United States. Earlier sections of this report 

presented discussions of the use of water for energy development and the use of energy for water development. Readily 

apparent in those discussions is the high degree of uncertainty 

in estimates of energy-related water consumption and waterrelated energy use. This uncertainty clouds our understanding 

of important issues and complicates efforts to ensure sustainable supplies of water and energy. This section addresses the 

earth science aspects of the water-energy nexus; it presents a 

review of current data-collection and research efforts and an 

examination of how enhanced efforts can reduce the uncertainty in our understanding of important water-energy issues 

and promote sustainable use of precious resources. Data 

collection, data interpretation, and research are all closely 

intertwined. For convenience, water- and energy-related issues 

are addressed in the following sections under the two broadly 

overlapping themes of monitoring and assessments and earth 

science research. 

Monitoring and Assessment

Monitoring Networks

Hydrologic, climatological, environmental, seismic, and 

other types of data are collected across the United States for a 

wide range of purposes, such as to check the weather, determine the current stage of a river, and identify the magnitude 

and location of an earthquake. In addition to providing a snapshot of current conditions, long-term data-collection networks 

provide a means for identifying trends and for calibrating 

computer simulation models that are used to estimate conditions at unmonitored sites and to predict future conditions. As 

such, monitoring networks are integral to our understanding 

of the past, current, and future effects of energy production on 

water and ecosystem resources. 

Data-collection networks exist at State, regional, and 

national levels in the United States. The national network most 

familiar to people is probably the National Weather Service 

(http://www.weather.gov/), a weather station network supported by the National Oceanic and Atmospheric Administration that provides precipitation, temperature, and other data 

from thousands of locations across the United States on a daily 

and sometimes real-time basis. This weather information is 

used by Americans who are curious about the day’s weather, 

by forecasters who predict weather patterns for coming days, 

and by climatologists who predict long-term climate trends. 

An example of a regional scale network is SNOTEL (http://

www.wcc.nrcs.usda.gov/snow/), a network supported by the 

National Resources Conservation Service for collecting data 

on snowpack and climatological parameters at over 600 sites 

in 13 western States. The original intent of the SNOTEL 

network was to provide data for estimating rates and volumes 

of snowmelt that could be used in decision-support models for 

optimizing storage and release from surface-water reservoirs. 

The data are still used for that purpose, but the data are also 

widely used for climate research. On a State level, Montana 

has a network of monitoring wells for assessing changes in 

groundwater levels related to coal mining and development of 

coalbed natural gas (Meredith and others, 2012). Data from 

networks such as these provide valuable insight on many 

water-energy issues; however, if data collection is too widely 

spread in space or time, localized effects of energy production 

may go undetected. Regardless of network extent, the integrity 

of any data can be guaranteed only if quality assurance and 

control protocols are in place and followed.

Hydrologic, ecosystem, and seismic data-collection networks can be expensive to operate and maintain, and often the 

benefits that they provide are not fully recognized. For these 

reasons, funding for these networks is often reduced in times 

of fiscal austerity. Such measures are unfortunate because 

monitoring networks serve a variety of interests. For example, 

water and ecosystem managers, agricultural planners, industrialists, environmentalists, and outdoor enthusiasts are among 

those who rely on consistent and available hydrologic data. 

Recently, common interests in water availability and quality 

have brought together diverse groups to support expanded 

monitoring in some regions of the United States in order to 

assess the potential effects of energy development. One such 

region is the Piceance Basin in northwestern Colorado (see 

Box O—Piceance Basin Water-Quality Data Repository).

A spring-fed stream in the Two-Medicine drainage of Glacier National 

Park. Springs offer services such as water for humans, vegetation, 

and local and migratory wildlife.

Continued on page 71
General extent of oil-shale 

deposits in the Green 

River Formation

Boundary of Piceance Basin 

in Colorado

Producing oil or gas well

EXPLANATION

Meeker

Glenwood

Springs

Rifle

Rangely

Grand Junction

Delta

MOFFAT

RIO BLANCO

GARFIELD

MESA DELTA

MONTROSE

OURAY

GUNNISON

PITKIN

Gu nnison River

White RiverWhite River

109° 108° 107° 106°

40°

39°

38°

+

Colorado River

0 25 50 MILES

0 25 50 KILOMETERS

Base from U.S. Geological Survey digital data, various scales, variously dated

Map area

COLORADO

70 The Water-Energy Nexus—An Earth Science Perspective

Piceance Basin Water-Quality Data Repository—A Tool for Water-Resource 

Monitoring Related to Energy Development

The Piceance Basin occupies about 25,000 km2 in 

northwestern Colorado (fig. O–1) and contains vast energy 

resources. Sediments of the Mesaverde Group and Wasatch 

Formation contain about 133 billion m3 of undiscovered 

natural gas (U.S. Geological Survey, 2003). Oil shale of 

the overlying Green River Formation contains an estimated 240 trillion L of oil (Johnson and others, 2009). 

Commercial production of natural gas in the basin began 

more than 50 years ago. As of 2012, there were more than 

12,000 producing oil and gas wells in the basin. Many of 

the gas wells are hydraulically fractured to increase gas 

production, which can require several million liters of 

water per well. Production of oil from shale is still largely 

a research effort on the part of energy companies because 

the oil shale was never buried deeply enough to generate oil; 

thus, the temperature of the shale must be raised in order to 

produce oil. Estimates of water consumption for oil shale 

development generally range from about 1 to 12 liters of water 

per liter of oil produced; however, these estimates are not well 

constrained because methods of production are still being 

developed (U.S. Government Accountability Office, 2011b). 

Nevertheless, these water-use estimates represent substantial 

quantities of water given the large volume of in-place oil.

Most of the basin has a semiarid climate, so water 

resources are limited. The primary sources of freshwater 

include major rivers such as the Colorado, Gunnison, and 

White, as well as bedrock aquifers and alluvial deposits along 

the rivers. Surface-water and groundwater resources in the 

Figure O–1. Location of producing oil and gas wells, oil shale deposits, and major rivers in the Piceance Basin, Colorado.
Science for Addressing the Water-Energy Nexus 71

Available Freshwater

As competition for water grows, the need for information and tools to aid water-resource managers also grows, 

yet a comprehensive assessment of water availability in 

the United States has not been made in more than 40 years 

(U.S. General Accounting Office, 2003). The U.S. Water 

Resources Council published a rudimentary national assessment in 1968 (U.S. Water Resources Council, 1968) and the 

more comprehensive Second National Water Assessment 

10 years later (U.S. Water Resources Council, 1978). 

A national assessment of water availability is a 

complex undertaking. At the time of the previous national 

assessments, water availability was viewed in comparatively simple terms. These early assessments focused 

largely on basic statistics about the quantities of water 

available for various human uses. Since then, competition 

for water resources has increased and more importance has 

been attached to the availability of water for environmental and ecosystem uses, in addition to human use. Likewise, concerns have grown about groundwater depletion, 

streamflow alteration, climate change and variability, and 

water-quality impairment. Awareness of the connectivity 

of surface water and groundwater and the links between 

water availability and the use of energy and other natural 

resources has also increased. 

The Secure Water Act, Subtitle F of the Omnibus 

Public Land Management Act of 2009 (Public Law 111-11; 

passed into law on March 30, 2009), helps address the need 

for more information. Section 9508 of the Act calls for 

the establishment of a “national water availability and use 

assessment program,” or a “national water census” (Alley 

and others, 2013). According to the Act, the water census 

should

Above: U.S. Geological 

Survey streamgage on 

the White River below 

Meeker, Colorado.

Right: Flaring of natural 

gas in the Piceance 

Basin.

basin support many uses in addition to energy development, including agriculture, urban and rural communities, 

industry, and terrestrial and aquatic ecosystems (Thomas 

and McMahon, 2012). There is concern that the availability 

and quality of water for these other uses could be affected 

as large-scale energy development continues.

A water task force consisting of citizens; local, State, 

and Federal governmental agencies; and energy companies 

collectively identified the need for a common repository 

for water-quality data collected by numerous monitoring 

programs that operate in the basin. The U.S. Geological 

Survey, in cooperation with more than two dozen partners, 

created a public, Web-accessible common data repository 

that combines water-quality data from industry, local, State, 

Federal, and other sources (http://rmgsc.cr.usgs.gov/aspbin/cwqdr/Piceance/index.shtml). The quality and completeness of the incoming data are reviewed, documented, 

and stored into a single uniform format. All available 

water-quality data have been evaluated to assess the current 

conditions of the region’s water resources (Thomas and 

others, 2013: Thomas and McMahon, 2012). Results of the 

assessment facilitate the development of regional monitoring strategies to fill identified data gaps and minimize 

redundancies in current and future water-resource monitoring. This common data repository for the Piceance Basin 

provides a valuable contribution to the planning, monitoring, conservation, and management of water resources as 

energy development continues.

Priorities for Assessing Freshwater 

Availability

• Develop methods for conducting a water census.

• Reduce uncertainty in watershed water-budget 

calculations.

• Establish a national groundwater monitoring 

network.

• Expand monitoring of surface water, groundwater, and water quality in areas of future energy 

development.

• Integrate models of water quality and ecosystem 

health.
0.0002 to 0.12

0.13 to 0.25

0.26 to 0.37

0.38 to 0.59

0.60 to 0.70

0.71 to 1.00

Water availability metric:

surface water

EXPLANATION

0 400 800 KILOMETERS

0 400 800 MILES

Base from Esri, 2013

Data from Tidwell and others, 2013

72 The Water-Energy Nexus—An Earth Science Perspective

• provide a more accurate assessment of the status of the 

water resources of the United States; 

• assist in the determination of the quantity of water that 

is available for beneficial uses; 

• assist in the determination of the quality of the water 

resources of the United States; 

• identify long-term trends in water availability; 

• use each long-term trend to provide a more accurate 

assessment of the change in the availability of water in 

the United States; and 

• develop the basis for an improved ability to forecast 

the availability of water for future economic, energyproduction, and environmental uses. 

The water census is intended to synthesize information at the 

regional and national scales and to report this information in 

a way that is useful to States and others responsible for water 

management and natural-resource issues. The water census is 

a collaborative effort involving the U.S. Geological Survey, 

the U.S. Bureau of Reclamation, other Federal and State agencies, universities, and additional organizations. Information 

provided by the census can be aggregated with socioeconomic 

information, such as data on food and energy production, to 

maximize its utility. Design and development of the water census is coordinated through the Federal Advisory Committee on 

Water Information (http://acwi.gov/). 

Much of the information in a national assessment of 

water availability pertains to water budgets for watersheds 

(fig. 32) and aquifers (Box B—Water Availability and Use 

in the United States). Water budgets account for the inputs 

to, outputs from, and changes in the amount of water stored 

in the various components of the water cycle over a fixed 

volume (such as a watershed) and a fixed time interval (such 

as a year). The water-budget components of most interest 

are precipitation, evapotranspiration, change in storage, and 

flow into and out of the watershed or aquifer. A long-term 

goal of the national water census is to provide measurements 

or estimates of these components on a monthly basis for all 

watersheds at the 12-digit hydrologic unit code scale (average 

drainage area of about 95 km2

) (Alley and others, 2013). A 

dedicated hydrologic data-collection network is a key element 

in efforts to achieve this goal, but given current measurement 

technologies, it is not practical to measure every water-budget 

component at each of these watersheds. Instead, hydrologic 

simulation models can be used to estimate components for 

many watersheds. Improvements in models and methods for 

collecting data, such as with satellite remote sensing, can 

enhance current capabilities. 

Figure 32. Surface-water availability as defined by a metric based on measured streamflow and current water use. High values 

(greater than 0.7) (in red) indicate areas of limited surface water availability. Water availability in this study was determined for 

watersheds at the 6-digit hydrologic unit code scale (average drainage area of about 22,000 square kilometers) in order to assess water 

availability for new thermoelectric power plants. (Tidwell and others, 2012, 2013)
Science for Addressing the Water-Energy Nexus 73

Uncertainty in water availability assessments is also 

a concern. Uncertainty is inherent in data collection, data 

interpretation, and in application of hydrologic models. Water 

management options can be evaluated more effectively if the 

uncertainty levels in all water-budget calculations are known. 

Development of improved methods for quantifying and reducing uncertainty in water-budget analyses of watersheds would 

be highly beneficial for a national water census. 

Water Quantity Monitoring

The U.S. Geological Survey, in collaboration with over 

850 Federal, State, and local agencies maintains the National 

Streamflow Information Program (http://water.usgs.gov/nsip), 

a surface-water gaging network that monitors streamflow at 

more than 8,000 sites nationwide. The streamflow information 

is vital for a number of purposes—assessing water availability, predicting the occurrence of and assessing the extent of 

floods and droughts, monitoring aquatic ecosystem habitat, 

designing bridges and conveyance structures, and identifying 

trends in streamflow that might be natural or that might result 

from human activity. Many of these purposes are linked to 

the water-energy nexus. Data from streamflow monitoring is 

needed to determine water availability for current and future 

energy production activities, such as cooling at thermoelectric 

power plants and fuel extraction, growth, and processing; to 

control withdrawals of surface water so as to preserve sufficient surface-water flow to support aquatic habitats; and to 

calibrate models used to predict the occurrence and severity 

of droughts, which can lead to reductions in the availability of 

power-plant cooling water. The accuracy of any predictions 

usually improves as the length of the period of data collection 

increases. Streamflow records also can be used to evaluate the 

effects of land-use changes related to energy production, such 

as those caused by mountaintop mining and the conversion of 

native grasslands to row crops for biofuels production.

Groundwater levels are measured at many thousands of 

observation wells across the United States. Measurements 

are made manually, at weekly to annual frequencies, and 

by automated continuous recorders. These wells belong to 

networks maintained by local, State, regional, or Federal agencies. Currently, there is no national groundwater monitoring 

network within the United States. Through the Groundwater 

Watch Program (http://groundwaterwatch.usgs.gov/), the 

U.S. Geological Survey maintains a database of groundwater 

levels for approximately 850,000 wells, but only about 20,000 

of those wells had water-level measurements in 2013, and 

even fewer wells (about 2,500) had daily or more frequent 

measurements. Measurements of groundwater levels are useful 

for assessing water availability and identifying natural trends 

and those related to human activities (fig. 33). In regard to 

the water-energy nexus, groundwater information is important for assessing water availability for energy development 

and for monitoring effects of energy operations such as coal 

mining, extraction of coalbed natural gas, irrigation of biofuel 

feedstock crops, and subsurface injection of wastewater and 

carbon dioxide. 

Groundwater levels typically change slowly, so years to 

decades of water-level measurements are required to evaluate 

the long-term effects of aquifer development, land-use change, 

and climate change. Ideally, a record of groundwater-level 

measurements would encompass the period between the natural state and the developed state of aquifer systems. A comprehensive water-level monitoring program would consider 

important aquifers within the United States and the way that 

they are affected by current and future groundwater development, major areas of groundwater recharge, and links with 

surface-water and water-quality monitoring. The Advisory 

Committee on Water Information has proposed the establishment of a national groundwater monitoring network in the 

United States (Subcommittee on Ground Water, 2013).

Water Quality Monitoring

The availability of water is determined by water quality as well as water quantity. High concentrations of many 

naturally occurring and synthetic substances can limit the 

suitability of water for some uses. The U.S. Environmental 

Protection Agency (2009) estimated that more than one-third 

of streams and rivers in the United States are impaired or polluted. Energy production is just one of many human activities 

that can lead to the contamination of water resources. 

Water quality monitoring supports multiple goals, such as 

safeguarding human and ecosystem health, assessing availability of water for specific uses, identifying causes of water 

contamination, and evaluating strategies for remediation of 

that contamination. With respect to the water-energy nexus, 

water-quality information is useful for determining whether or 

not water from a particular source can be used for a specific 

application, such as irrigation or cooling. The information is 

also useful for identifying the occurrence, extent, and possible 

cause of contamination generated by energy-related operations. The water quality of surface waters and groundwater is 

monitored through two approaches: collection and analysis 

of discrete water samples and continuous in-place monitoring (for some parameters). Discrete samples can be analyzed 

in the laboratory for hundreds of physical, chemical, and 

biological properties. Continuous recorders, on the other hand, 

are capable of measuring only a handful of properties (such 

as temperature, specific conductance, pH, dissolved oxygen 

concentration, and nitrate concentration), but data from these 

recorders can be obtained at frequencies as high as every 

minute. Both of these approaches provide useful information 

for determining the current state of water quality and for identifying trends over time. Data from continuous recorders and 

measured streamflow can be used to estimate concentrations 

and loads for unmeasured constituents based on regression 

equations developed for individual sites (see, for example, the 

real-time water quality data available for Kansas: http://nrtwq.

usgs.gov/ks/). 
105° 97° 96° 104° 103° 102° 101° 100° 99° 98°

43°

42°

41°

40°

39°

38°

37°

36°

35°

34°

33°

32°

Canadian River

Arkansas River

South Platte River

Republican River

North Platte River

Platte River

OKLAHOMA

NEW MEXICO

COLORADO

KANSAS

WYOMING

SOUTH DAKOTA

TEXAS

NEBRASKA

U

U

U

U

U

U

U

3 to 8

-1.5 to 3

8 to 15

More than 15

Area of little or no saturated thickness

Area of water-level changes with few 

predevelopment water levels—(Lowry 

and others 1967; Luckey and others, 1981; 

University of Nebraska–Lincoln, 

Conservation and Survey Division, 2012)

County boundary

Faults—U, upthrown side U

EXPLANATION

Water-level change—In meters

More than 46

30 to 46

15 to 30

8 to 15

3 to 8

1.5 to 3

Decline

No substantial change

Rise

-1.5 to +1.5

Aquifer boundary from Qi (2010); areas of little or no saturated 

thickness and faults from Gutentag and others (1984) 

and Cederstrand and Becker (1999a, 1999b) 

Base from U.S. Geological Survey digital data, 2001, 1:2,000,000

Albers Equal-Area Conic projection, standard parallels 29o 30' and 45o 30', central meridan -101o

North American Datum of 1983 (NAD 83)

0 25 50 75 100 MILES

0 25 50 75 100 KILOMETERS

74 The Water-Energy Nexus—An Earth Science Perspective

Figure 33. Water-level changes in the High Plains aquifer, from predevelopment to 2011 (McGuire, 2013). The High Plains Regional 

Groundwater Level Monitoring Network includes about 9,000 wells and is perhaps the largest regional network in the United States. 

Water levels in wells in the network are measured annually, predominantly by local and State agencies. (U.S. Geological Survey, 2014b)
Science for Addressing the Water-Energy Nexus 75

Water-quality monitoring networks usually are operated 

at local and State levels. The collected data, which include 

biological and chemical analyses of water samples and fish 

tissue, often are stored in the U.S. Environmental Protection 

Agency STORET (Storage and Retrieval) database. Biennial 

assessments are conducted by each State using these data and 

additional information obtained from predictive models and 

surveys of land use and ecosystems (U.S. Environmental Protection Agency, 2013c). In collaboration with other agencies, 

the U.S. Geological Survey operates continuous water-quality 

recorders at about 1,700 sites across the country; in addition, 

discrete samples are collected and analyzed at many sites 

under programs such as the National Water-Quality Assessment (NAWQA) Program (http://water.usgs.gov/nawqa/) and 

the National Stream Quality Accounting Network (http://

water.usgs.gov/nasqan). The NAWQA program supports 

long-term monitoring of water quality and aquatic ecosystem 

health, research on causes and effects of water contamination, 

and analyses of trends. Water quality data in U.S. Environmental Protection Agency, U.S. Geological Survey, and 

U.S. Department of Agriculture databases can be accessed 

through the Water Quality Portal (http://www.waterqualitydata.us/). 

Models are important tools for characterizing water quality and ecosystem health. Because of practical considerations, 

water quality can be directly monitored at only a limited number of sites, but models can be used to gain an understanding 

of water quality at unmonitored sites. Models are also useful 

for identifying factors that control contaminant transport and 

for evaluating options for remediation of contaminated sites. 

Water quality studies would benefit from development and 

application of models that are capable of integrating information on water movement, chemistry, biology, habitat, and land 

and water use to provide improved predictions of the effects of 

natural phenomena and human activities on water quality and 

ecosystem health. 

Collection and analysis of discrete water-quality samples 

can be expensive, which could place limits on the number of 

sites and frequency of sampling in a network. Water temperature, however, can be continuously monitored at a relatively 

low cost. Water-temperature data are important for assessing 

rates of climate change and the health of aquatic ecosystems. 

They are also important for thermoelectric power plants; withdrawals for cooling may be restricted if water temperatures 

exceed regulatory limits. A number of networks have been 

established in parts of the United States specifically to monitor 

stream temperatures (U.S. Forest Service, 2014).

Determining the effects of human activities on the water 

quality of any hydrologic system requires insight on the water 

quality of that system prior to the time at which human activities were initiated. Baseline, or background, water-quality data 

can provide that insight, but unfortunately such data are scarce 

for shallow aquifers in many regions of oil and gas development. Moreover, existing wells with background data are not 

always suitable for monitoring effects of energy development 

because wells may not be located proximate to energy operations or the period of data collection may not be long enough 

to detect contamination, should it occur (McMahon and others, 2013). Understanding the hydrologic framework in which 

wells are located is important for evaluating the usefulness of 

existing wells as monitoring points. 

Water Use

The use of water by humans is an important component of the global water cycle. Understanding the relation 

between water use and the water cycle can shed light on how 

human activities affect climate and how both human activities 

and variations in climate affect water availability. As such, 

water-use information is important in many fields. In particular, information on rates of water withdrawal, conveyance, 

consumptive use, and return flow are vital to understanding 

the links between water availability and energy production. 

Regular assessments of water use provide trend information 

that can support planning for future water needs. Since 1950, 

the U.S. Geological Survey has compiled assessments of 

water use in 5-year intervals and published results in a series 

of reports entitled “Estimated Use of Water in the United 

States.” These assessments are collaborative efforts involving 

all 50 States and multiple Federal agencies. Water-use data are 

provided for eight distinct categories: public supply, domestic 

supply, irrigation, livestock, industrial, aquaculture, mining, 

and thermoelectric power. The most recent water use report 

covered years 2006–2010 (Maupin and others, 2014).

Thermoelectric power represents about 45 percent of 

water withdrawals in the United States (Maupin and others, 2014). Nearly all of the water withdrawn for this use is 

returned to a surface-water body and is readily available for 

other uses. For the 2000, 2005, and 2010 water-use reports, 

consumptive water use by thermoelectric power plants was 

not reported. Future plans call for incorporating consumptive 

use data into the national water-use database maintained by 

the U.S. Geological Survey (http://waterdata.usgs.gov/nwis/

wu) (M.A. Maupin, U.S. Geological Survey, written commun., 

2014). Methods for estimating power-plant water consumption 

can be improved by incorporating information on plant characteristics, power generation, fuel use, type of cooling system, 

and climate. Better techniques for estimating consumptive 

use of power plants will account for the evaporation caused 

Priorities for Monitoring Water Use

• Develop improved methods for measuring or estimating water withdrawal and consumption for energy 

use, especially by hydroelectricity generation and 

biofuels production.
Seminoe Dam and power plant, Wyoming.

76 The Water-Energy Nexus—An Earth Science Perspective

by the increased temperature of water used for cooling after 

it is returned to a stream or reservoir (Diehl and others, 2013; 

Diehl and Harris, 2014). 

Estimation of water consumption rates for generating 

hydroelectric power and for growing biofuels poses unique 

problems. The amount of water that evaporates annually from 

reservoirs that feed hydroelectric plants may be larger than the 

total amount of water consumed for all other electricity-generating operations in the United States, even though hydroelectricity represents only 7 percent of all generated electricity 

(table 4). However, uncertainty is inherent in estimates of 

water consumption at hydroelectric plants because evaporation rates are difficult to accurately determine and few studies 

have been conducted on reservoirs associated with these 

plants. Even if accurate estimates of reservoir evaporation 

were available, the question of whether all of the evaporation 

should be assigned to the generation of electricity needs to be 

addressed (Bakken and others, 2013). Dams and reservoirs are 

constructed for multiple purposes; portions of the evaporated 

water might more correctly be assigned to uses such as water 

supply, recreation, or flood control. The development and 

application of a uniform method for allocating water consumption from reservoirs would help to reduce the uncertainty 

associated with water consumption by hydroelectric plants. 

With regard to biofuels, water use is associated primarily with 

irrigation. Estimates are available for the amount of irrigated 

acreage of corn and soybean crops in the United States, but 

the percentages of these irrigated crops that are processed into 

bioethanol or biodiesel are not known. This uncertainty limits 

our ability to accurately determine overall water consumption 

rates for the transportation sector.

Ecosystems

Ecosystems are communities of plants, animals, and 

microbes that live and interact with nonliving components 

such as water, air, and soil minerals. They range in size from 

a microscopic area to a puddle of water to an ocean or a 

continent. The Earth itself can be viewed as an ecosystem. The 

structures and processes of ecosystems provide a number of 

beneficial services to humans, including purification of air and 

water, mitigation of droughts and floods, generation and preservation of soils and renewal of their fertility, detoxification 

and decomposition of wastes, pollination of crops and natural 

vegetation, dispersal of seeds, cycling and movement of nutrients, and control of the vast majority of potential agricultural 

pests (Daily, 1997). Additional services contribute to human 

enjoyment, such as the aesthetic qualities provided by forests 

and water bodies as well as recreational and cultural opportunities. The health of ecosystems and the benefits they provide, 

however, are affected by human activities. Energy and water 

development can result in changes in land use, water quantity 

and quality, and air quality. These changes can adversely affect 

ecosystems.

The wide range in spatial scales associated with ecosystems has led to a variety of approaches for the assessment 

and monitoring of their health. There are no national-level 

ecosystem monitoring networks, and there are no standard 

metrics for measuring ecosystem health, but there are a 

number of smaller programs that provide important information on ecosystems. Within the United States, each State has a 

wildlife management program, with the Federal government 

providing oversight for the management of endangered species (U.S. Fish and Wildlife Service, 2014). Surveys for fish, 

big game, and waterfowl are conducted regularly to support 

management programs that include fishing and hunting. For 

aquatic ecosystems, water quality analyses, as described previously, provide important information on ecosystem health. 

Within the Department of the Interior, two agencies have 

established Inventory and Monitoring programs to monitor 

Priorities for Assessing Monitoring 

Ecosystems

• Standardize methods for assessing ecosystem 

services.

• Adapt monitoring programs to include information 

that can be used to quantify and value ecosystem 

services.

• Develop decision-support tools to allow resource 

managers to include ecosystem services in costbenefit analyses of energy development scenarios.
Evanston

Kemmerer

Pinedale

Rock Springs

111°W 110°W 109°W 108°W 107°W

43°N

42°N

41°N

0 25 50

Kilometers

Surface Total

administration acres

U.S. Bureau of Land Management (BLM).....7,985,500

Private...........................................................4,262,200

U.S. Forest Service.......................................2,306,800

Wyoming State Land........................................559,900

U.S. Bureau of Reclamation.............................220,600*

U.S. Fish and Wildlife Service............................16,400*

National Park Service...........................................8,400*

Surface Water

WYOMING

191

80

Data provided by the Bureau of Land Management

*Depicted in black in the pie graph

Science for Addressing the Water-Energy Nexus 77

ecosystems on lands they manage: the National Park Service 

(https://science.nature.nps.gov/im/) and the U.S. Fish and 

Wildlife Service (http://www.fws.gov/Refuges/NaturalResourcePC/IandM/). These programs were set up to assess the 

effects of climate change and land-use change on ecosystems. 

On the national level, the National Ecological Observation 

Network (NEON, http://www.neoninc.org) is currently (2014) 

being established with funding from the National Science 

Foundation. The goal of NEON is to monitor the causes and 

effects of climate change, land-use change, and invasive 

species on ecosystems in the United States. Collection of 

atmospheric, soil, organismal, and aquatic data is planned at 

60 terrestrial and 36 aquatic sites across the United States. 

The Wyoming Landscape Conservation Initiative (WLCI, 

http://www.wlci.gov/) is a unique endeavor supported by the 

U.S. Bureau of Land Management and several Federal, State, 

and local agencies. The WLCI is a long-term science based 

effort to assess and enhance aquatic habitats while facilitating 

responsible energy and agricultural development in a large 

area of southwestern Wyoming (fig. 34). The WCLI addresses 

management needs identified by its partners through a program of monitoring and research. Approaches for addressing 

those needs include developing conceptual models for 

understanding ecosystem function, identifying key drivers of 

change affecting WLCI ecosystems, and conducting scientific 

monitoring and experimental studies to better understand 

ecosystems processes, cumulative effects of change, and the 

effectiveness of habitat treatments (Bowen and others, 2009).

A desert spring offers 

services such as water 

for humans, vegetation, 

and local and migratory 

wildlife. Cultural and 

aesthetic aspects of such 

features are cherished 

by many humans. Lack of 

consistent methodology 

inhibits our ability to 

quantify the amount 

of services provided 

by ecosystems and to 

determine the value of 

those services.

Figure 34. The Wyoming Landscape Initiative area, including surface jurisdiction. (Bowen and others, 2009)
Depth to saline groundwater, in meters

Less than 152

152 to 304

Greater than 304

Inadequate information

EXPLANATION

Data obtained from programs such as these and from 

site- and ecosystem-specific assessments can be useful for 

assessing the effect of energy development. However, the lack 

of a consistent, standardized method for measuring ecosystem services hinders efforts to develop a universally accepted 

accounting system (Boyd and Banzhaf, 2006) in which, for 

example, the value of oil or natural gas extracted at a particular location could be compared with the value of the ecosystem services that were lost as a result of that extraction. Haines 

and others (2013) present a framework that can be used to 

generate quantitative assessments of the effects of fossil-fuel 

extraction on ecosystems. Ideally, new tools will be developed to determine equivalent economic values of affected 

ecosystem services in a consistent and unbiased approach, 

which could lead to the inclusion of cost-benefit analyses into 

decision-support software and, in turn, would allow for direct 

comparison of environmental costs of different development 

schemes (Darius Semmens, U.S. Geological Survey, written 

commun., 2014). Resource managers could use these comparisons to select development scenarios or management strategies 

to reduce adverse effects on ecosystem services. 

Saline Groundwater Availability

Concern about the sustainability of freshwater supplies 

has fostered interest in the use of nontraditional water sources. 

Saline groundwater (water with total dissolved solids concentration greater than 1,000 mg/L) is increasingly being viewed 

as a valuable resource that can be used in place of freshwater 

for many purposes. Desalination, for example, offers the possibility of producing drinking water from saline groundwater 

or seawater. In 2007, the city of El Paso, Texas, brought on 

line the largest inland desalination plant in the United States, 

producing about 100 million L of water daily (El Paso Water 

Utilities, 2007). Desalination is an energy-intensive process; 

however, treatment to the level required by drinking-water 

standards is not always necessary. With minimal or no treatment, saline water can be used for a number of energy-related 

purposes, including drilling and hydraulic fracturing. In addition to being tapped as a source of groundwater, saline aquifer 

systems are widely used for the disposal of wastewater. The 

El Paso desalination plant disposes of the liquid concentrate 

78 The Water-Energy Nexus—An Earth Science Perspective

Priorities for Assessing Saline 

Groundwater Availability

• Determine the distribution and physical and geochemical properties of saline aquifers.

• Improve our understanding of the connection 

between freshwater and saline aquifers.

produced by the reverse osmosis process by deep well injection. Information on the locations and characteristics of saline 

aquifer systems can promote more efficient and environmentally sound operations. 

Areas of aquifer systems containing saline water commonly are connected hydraulically to areas of the same system 

that contain freshwater. Thus, development of one resource 

may affect the other. Little information is available on the 

hydrogeology of the parts of most aquifers that contain saline 

water (fig. 35) because of limited interest in saline groundwater in the past. Improved understanding of the hydrogeology of these systems can provide insight on the volumes of 

water that could be extracted, the rates at which wastewater 

and carbon dioxide could be injected, and the potential for 

induced seismic activity and contamination of freshwater aquifers from injection operations. 

Geochemical data on saline groundwater resources 

are also scarce. The chemistry of saline water can affect the 

usability of the water. Saline groundwater can contain high 

concentrations of naturally occurring constituents, such as 

arsenic and radioactivity, that can limit the allowable uses of 

the water. Water chemistry must also be considered in design 

and planning of wastewater injection operations; incompatible 

chemistries of native formation water and injected waters can 

lead to unintended reactions such as precipitation of solids 

that can reduce aquifer permeability and clog well screens 

(Kharaka and others, 1997). An improved knowledge base 

can better define the distribution and physical and chemical 

characteristics of saline aquifer systems and groundwater and, 

Figure 35. Generalized map of the depth to saline groundwater 

for the conterminous United States. This map provides a 

preliminary perspective on the location of saline groundwater 

resources, but it contains limited information about critical 

factors required to understand the development potential of the 

resources, such as aquifer permeability and well yields. (Modified 

from Feth and others, 1965)
in so doing, support more accurate predictions of the effects 

of saline-water extraction and wastewater and carbon dioxide 

injection on the aquifer system and the environment. In addition to helping guide development and protection of resources, 

this information can provide a scientific basis for regulatory 

and policy issues. 

Fossil Fuels and Uranium

The United States accounts for about 18 percent of 

worldwide energy consumption (International Energy Agency, 

2012a). Knowledge about our domestic energy potential from 

fossil-fuel and uranium sources is important for planning for 

future energy development. For example, rapid expansion of 

shale gas and tight oil over the past decade has dramatically 

affected the Nation’s energy outlook. Producing fundamental data on the quantity and location of undiscovered energy 

resources, such as oil, natural gas, and coal, is a core activity of the U.S. Geological Survey (http://energy.usgs.gov/). 

This information is conveyed in the form of assessments of 

undiscovered, technically recoverable energy resources, that 

is, resources that are yet to be discovered but, if present, can 

be extracted using existing technology (see, for example, Scott 

and Luppens, 2013). The assessment methods are probabilistic to take into account uncertainty; they provide estimates of 

upper and lower bounds around a median value. The assessment data, when combined with data generated by the Bureau 

of Ocean Energy Management (http://www.boem.gov) and 

the Energy Information Administration (http://www.eia.gov), 

provide a broad perspective of available energy resources of 

the United States. 

As new technologies evolve and additional information 

becomes available, assessments of energy resources need to 

be updated. In some cases, revised assessments can have a 

significant effect on resource development. In the wake of 

enhanced technologies such as hydraulic fracturing and directional drilling, the assessed undiscovered, technically recoverable oil resources of the Bakken-Lodgepole total petroleum 

system (fig. E–1) have increased from 24 billion L in 1995 

to 477–684 billion L in 2008 (Pollastro and others, 2008) to 

0.8–1.8 trillion L of oil in 2012 (Gaswirth and others, 2013). 

This system is currently the largest assessed, undiscovered 

unconventional oil resource in the United States. Assessment methods themselves undergo periodic revision to reflect 

improvements in estimation techniques and additional information that may become available. The methodology used by 

the U.S. Geological Survey for the assessment of unconventional hydrocarbon resources was revised in 2005 and again in 

2010 (Charpentier and Cook, 2010). 

Additional beneficial uses of energy assessments should 

be explored. Many questions related to development of 

unconventional oil and natural gas resources remain unanswered: How much water is needed for drilling and wellbore 

stimulation? How much fresh and saline water is currently 

being used for these purposes? What are the impediments to 

using recycled or produced water for these purposes? Linking 

energy assessments to assessments of water, ecosystems, and 

other resources can be beneficial in a number of ways. The 

creation of a methodology for assessing the lifecycle water use 

for the development of unconventional oil and gas resources 

would benefit energy, water-resource, and ecosystem managers, as well as energy and water developers and water users. 

A better understanding of water use on a well-by-well basis 

would lead to improved estimates of water use at the regional 

and national scales. A consistent accounting of life-cycle water 

use would facilitate cooperative planning of energy and water 

development activities and thus help to avert conflicts among 

different water users (Haines and others, 2014; Nicot and 

others, 2014).

Geothermal Resources

The geothermal systems that currently provide electricity to the power grid are the systems that were the easiest 

to discover and develop. Other hydrothermal fields, whose 

surface expression is less obvious, might prove to be good 

sources for electricity generation. Undiscovered moderate- to 

Science for Addressing the Water-Energy Nexus 79

Priorities for Assessing Fuel Resources

• Update assessments when new energy-development techniques emerge. 

• Develop improved assessment techniques.

• Integrate water and ecosystem assessments into 

energy resource assessments.

Priorities for Assessing Geothermal 

Resources

• Identify untapped traditional hydrothermal fields.

• Develop a fundamental understanding of the way in 

which geothermal systems function, including water 

and energy balances and their relation to seismic 

activity.

• Identify favorable sites for enhanced geothermal 

system power plants and determine the water requirements and potential seismic hazards.
Operational water requirements for enhanced geothermal 

resources are largely unknown and will depend on the cooling 

methods that are employed. The requirements could be similar 

to those for traditional binary geothermal systems, but with 

additional water required during initial development of the site 

to enhance permeability.

Planning and development of future enhanced geothermal 

systems can benefit from a wide range of research. Identification of potential power plant sites relies on continued 

assessments of geothermal resources and development of 

more sophisticated assessment methods. Accurate estimates 

of water requirements for developing these systems as well 

as local assessments of available water are also critical factors for siting new plants. Beyond that, improved techniques 

for enhancing the permeability of host rocks could open 

up additional areas for potential development of enhanced 

geothermal systems.

Management of both traditional and enhanced geothermal 

systems can benefit from research to better understand the fundamental nature of geothermal reservoirs and the way in which 

they function. An understanding of the geofluid balance, the 

energy balance, and the geomechanical features of a reservoir 

(such as structure, lithology, permeability, fault and fracture 

characteristics, and stress) can lead to improved efficiency of 

operation as well as an extended life for the reservoir. Measurements of seismic activity, when used in conjunction with 

this information could substantially enhance our understanding 

of the relation between plant operation and induced seismic 

activity and, in so doing, lead to safer plant operation.

Induced Seismicity

Earthquakes occur naturally. They can also be induced by 

a number of human activities including nuclear-weapons testing, reservoir construction, and energy-related activities such 

as wastewater and carbon dioxide injection and development 

of geothermal systems. Ascertaining whether human activity 

is the cause of an earthquake can be difficult. It appears likely, 

however, that induced seismicity from energy operations has 

contributed to the trend, since 2001, of increasing numbers of 

earthquakes of magnitude 3 or higher in the central and eastern 

United States (fig. 36) (Ellsworth, 2013).

80 The Water-Energy Nexus—An Earth Science Perspective

high-temperature geothermal resources could exist in regions 

such as the Basin and Range Province, the Cascade Range, 

the Salton Trough, and the Rio Grande Rift, as well as deep 

sedimentary basins (Duffield and Sass, 2003). Undiscovered 

traditional hydrothermal fields in the United States could 

be capable of producing 30,000 MW of electricity, or about 

15 times the generating capacity of currently operating 

geothermal plants (Williams and others, 2008). A program of 

targeted geophysical studies and drilling would help identify 

these potential sites.

Harnessing geothermal energy relies on the presence 

of high subsurface temperatures, a geofluid, and a highly 

permeable structure in the subsurface that allows for rapid 

movement of the geofluid. Many areas of the United States 

have subsurface temperatures that are sufficiently high to 

allow geothermal development, but because of low permeability in these areas, geofluids cannot be rapidly circulated. 

Enhanced geothermal systems have been proposed, however, whereby the permeability of the subsurface would be 

increased (perhaps by hydraulic fracturing) to allow rapid 

circulation of geofluids. The potential for enhanced geothermal systems in the United States is substantial. Enhanced 

systems could be capable of producing up to 500,000 MW of 

electricity, equivalent to about one half of the entire electricity-generating capacity of the United States (Williams and 

others, 2008). Enhanced geothermal systems are simple in 

concept, but development of these systems on a commercial 

scale has proved to be challenging. The 1.7-MW Desert Peak 

2 plant in Nevada, which came on line in April of 2013, is the 

first commercial enhanced geothermal system power plant 

in the United States (U.S. Department of Energy, 2013a). 

In addition to its use in the production of electricity, geothermal 

energy can be used directly to heat buildings, streets, and sidewalks. 

Energy from a geothermal reservoir that lies at a depth of about 900 m 

beneath Boise, Idaho, is used to heat more than 400 buildings in the 

city, including the State Capitol Building. Geothermal heat pumps are 

used in many areas of the United States to supplement both heating 

and cooling systems for residential, commercial, and industrial 

buildings.

Priorities for Studying Induced Seismicity

• Expand seismic monitoring in areas of energy development.

• Improve our understanding of factors that contribute 

to induced seismic activity.
0

200

400

600

800

1,000

1,200

1,400

1970 1980 1990 2000 2010

Earthquake count

Year

Dedicated networks of seismometers exist across the 

United States and have been operational for many years. These 

networks serve two primary purposes: monitoring earthquake 

and volcanic activity and conducting research on Earth’s fundamental geological structure and processes. The Advanced 

National Seismic System (ANSS, http://earthquake.usgs.

gov/monitoring/anss/) is a partnership of the U.S. Geological 

Survey, academia, other government agencies, and industry 

that monitors seismic activity across the United States. Since 

its inception in 2000, funding has provided for the installation of more than 700 fixed-position stations for collecting 

high-quality seismic data to serve the needs of the emergency 

management and response, engineering, and scientific communities in regard to earthquake and volcanic activity. The Incorporated Research Institutions for Seismology (IRIS) supports 

USArray (http://www.usarray.org/), which is another array 

of transportable seismometers; these sensors are deployed for 

periods of 1 to 2 years to provide more detailed spatial coverage than can be obtained with the ANSS network. Because of 

the wide spacing between sensors in the networks and the fact 

that earthquakes of magnitudes less than 3 are typically not 

reported (Ellsworth, 2013), these networks are not ideal for 

detecting seismic activity induced by energy operations. However, because of the fortuitous deployment of seismometers in 

the USArray network, researchers recently were able to link 

the magnitude, timing, and location of earthquakes in parts 

of Oklahoma with operations at nearby subsurface injection 

Science for Addressing the Water-Energy Nexus 81

wells, thereby suggesting that wastewater injection triggered 

the earthquakes (Keranen and others, 2013).

Enhanced monitoring networks (where earthquakes of 

magnitudes less than 3 can be monitored) in the vicinity of 

energy operations would be beneficial for safety, regulation, 

and research purposes; more refined data would facilitate 

improved procedures for injection of wastewater and management of geothermal systems. For example, rates of wastewater 

injection might be reduced if nearby seismic activity reaches 

a certain magnitude. Such “traffic light” systems have been in 

use at a number of facilities for many years (Ellsworth, 2013). 

When combined with additional information on hydrogeology, 

stress and pressure conditions, withdrawal and injection rates 

and volumes, and presence and characteristics of nearby faults, 

enhanced monitoring of seismicity can lead to improved 

understanding of the causes of induced seismic activity and 

ultimately, perhaps, to development of tools for predicting and 

preventing the occurrence of induced earthquakes. 

Data Analysis Tools

Monitoring consists of more than just collecting data. To 

be of use, the collected data must be analyzed, first in order to 

assure the quality of the data and subsequently to identify any 

underlying spatial or temporal trends in the data. Data analysis 

tools are integral components of successful monitoring networks. These tools usually consist of protocols and statistical 

and numerical computer programs. In addition to supporting 

quality assurance and interpretation of data, these tools can 

help optimize network performance in terms of identifying 

important locations for collecting data and types of data that 

are collected. The tools can also serve as important components of decision-support systems that are used to manage 

natural resources. For example, incorporation of ecosystems 

data into decision-support software can enable managers to 

evaluate the ecological tradeoffs of various energy-development alternatives (Haines and others, 2013).

Computer simulation models are valuable tools for data 

analysis; examples of simulation models include groundwater flow models, reservoir management models, and 

ecosystem models. Monitoring and simulation modeling are 

Figure 36. Cumulative count of earthquakes with magnitude (M)

greater than 3 in the central and eastern United States, 

1967–2012. The dashed line corresponds to the long-term rate of 

21.2 earthquakes per year. (Ellsworth, 2013)

Priorities for Developing Analytical Tools

• Develop techniques to optimize network design.

• Improve computer simulation and decision-support 

models.

• Identify indicator or “tracer” characteristics for tracking contaminants.
Long-term monitoring networks

(water levels, streamflow, and water quality)

Short-term geologic and hydrologic studies

Conceptual model of

hydrogeological 

system

Numerical

groundwater 

flow model

Past Present Future

Time (not to scale)

82 The Water-Energy Nexus—An Earth Science Perspective

Naturally occurring methane is more 

prevalent in groundwater and surface water 

than previously assumed, so the presence 

of methane in a stream-water sample is not 

in and of itself evidence of human-induced 

contamination. Information on isotopic 

composition of carbon and hydrogen in 

methane could aid in identifying sources of 

methane in groundwater. 

Figure 37. A framework for the integration of groundwater 

monitoring and groundwater flow modeling. The top row signifies 

a long-term network that is systematically monitored over time. 

The second row represents the development of models and their 

periodic updates in order to advance the understanding of how 

the aquifer system responds to human development, integrating 

new information, and addressing new questions as they arise. 

The vertical arrows represent a feedback loop in which long-term 

monitoring is used as input to modeling and modeling is used to 

evaluate long-term monitoring networks. (Modified from Alley, 

2006) 

complementary activities. Data are important for building conceptualizations of real systems and for calibrating computer 

simulation models, and simulation results provide feedback 

and insights into the adequacy of and gaps in monitoring data. 

An idealized framework for the integration of monitoring and 

modeling in the context of regional groundwater studies is 

illustrated in figure 37. Ideally, monitoring and modeling are 

part of a dynamic process in which the model and the monitoring networks are periodically updated based upon their 

synergistic output. Improved simulation models could provide 

more realistic representations of processes and could quantify 

uncertainties both in our knowledge of those processes and 

in simulation results. Results from these models can allow 

managers to predict where and when effects of energy operations might be realized and how those effects might be best 

mitigated.

Trends in environmental data can result from natural 

processes and from energy development or other human 

activities. Natural variations in shallow groundwater chemistry, for example, can complicate efforts to distinguish between 

natural, unaffected groundwater and groundwater that has 

been contaminated by energy-related activities. This problem 

can be alleviated if certain physical, chemical, or biological 

traits in data can be uniquely associated with specific energyrelated activities and if those traits or “tracers” can be incorporated into network data-collection schemes. For example, most 

people can sense a leak in the natural gas line in their home 

by a familiar odor. Natural gas itself is odorless, so energy 

companies mix a chemical (methyl mercaptan) into the gas 

that they deliver to homes and businesses to produce an odor 

that makes leaks easy to detect. Environmental tracers are used 

in much the same way. Tracers can be specific compounds or 
EXPLANATION

1850 1900 1950 2000

Temmperature anomaly, in degrees Celsius0.6

0.4

0.2

0.0

-0.2

-0.4

-0.6

GISS

HadCRUT4

MLOST

EXPLANATION

Global mean sea level anomaly,

in millimeters

Year

-100

-50

0

50

100

150

200

1880 1900 1920 1940 1960 1980 2000

Church and White, 2011

Jevrejeva and others, 2008

Ray and Douglas, 2011

A

B

isotopic ratios of compounds that are in extracted fuels, native 

groundwater, injected wastewater, or geologic formations. 

Chemicals in fluids used in drilling, extraction, and hydraulic 

fracturing operations may also be useful as tracers. The identification of new tracers that can be used to study the effects 

of energy development on water and ecosystem resources and 

the incorporation of these tracers into the analytical schedules 

of water-quality monitoring programs would benefit a diverse 

group, including homeowners, ecosystem managers, waterresource managers, and energy-resource developers.

Research

Climate Change

Water and energy are intrinsically linked with climate 

through a variety of feedback mechanisms. Climate drives 

Earth’s water cycle and, as such, is the single most important 

factor controlling long-term water availability. At the same 

time, water use and land use can influence climate. Energy 

production and use also affect climate. Over the course of the 

past 100 years, the Earth’s average surface temperature has 

increased by about 1 °C, and global average sea level has risen 

steadily (in part due to melting snow and ice fields) (fig. 38). 

These trends result, at least partially, from energy production 

and use, primarily the combustion of fossil fuels and the subsequent emission of greenhouse gases, such as carbon dioxide 

and nitrous oxide, to the atmosphere (Intergovernmental Panel 

on Climate Change, 2013). Changes in climate and subsequent 

changes in water availability could place constraints on future 

options for energy production and use (U.S. Department of 

Energy, 2014).

Predictions of future climate trends generated with various global circulation models differ in the details, but consistent patterns appear for many regions. Of particular interest 

Science for Addressing the Water-Energy Nexus 83

Priorities for Studying Climate Change 

and Its Effects

• Reduce uncertainty in our understanding of past 

and future climates.

• Determine the effects of climate change on water 

resources (including the magnitude and frequency 

of floods and droughts) and ecosystems.

• Improve our understanding of the carbon cycle 

and its relation to climate.

• Evaluate the viability of geologic carbon sequestration.

Figure 38. A, Annual global mean surface temperature 

anomalies from three data sets (HadCRUT4, GISS, and NCDC 

MLOST), and B, annual global mean sea level (GMSL) anomalies 

reconstructed from tide gages by three different approaches. All 

anomalies are relative to corresponding averages for the period 

1961–1990. (Intergovernmental Panel on Climate Change, 2013)

are the trends for the southwestern United States—temperature 

increases of 1 to 4 °C by the end of the 21st century (fig. 39) 

and slight decreases in precipitation (Intergovernmental Panel 

on Climate Change, 2013). The southwestern United States, 

with its semiarid to arid climate, already has limited water 

resources, but the population growth, commensurate increases 

in energy requirements, and increases in extraction of hydrocarbon fuels expected in the coming decades will stress those 

resources even further. The rising demand for water for energy 

production in this region must somehow be resolved with 

potentially reduced amounts of available water. The benefits 

of collaborative planning among energy and water providers and regulators are apparent (Hightower and Pierce, 2008; 

U.S. Department of Energy, 2014). 
84 The Water-Energy Nexus—An Earth Science Perspective

A recent study outlined how the hydrologic effects of 

climate change can affect energy production (U.S. Department 

of Energy, 2013b):

• The thermal efficiency of thermoelectric power plants 

and the transmission efficiency of electric grid networks would decline with increasing temperatures, 

resulting in more fuel consumption to produce a fixed 

amount of electricity. 

• Decreased water availability could lead to reductions in 

electricity generating capacity. 

• Hydroelectric power plants could see a reduction in 

electricity generation if droughts become more common. 

• Increased temperatures would be accompanied by 

higher rates of potential evapotranspiration. 

• Greater evaporation from reservoirs would mean 

increased water intensity for hydroelectricity. 

• Increased storm intensities could lead to enhanced risk 

of damage to water and energy infrastructure. 

• The vulnerability of coastal infrastructure to damage 

from rising sea levels might increase. 

• Thawing permafrost in arctic regions would require 

modification of the methods used to extract hydrocarbon fuels in those regions.

Understanding the links among climate change, water, 

and energy requires some insight into past and future climate 

patterns, but this insight can be difficult to develop (Burkett 

and others, 2013). Hydrologic systems respond to short-term 

variability in weather patterns and long-term climate trends. 

Distinguishing between these two phenomena, although a 

difficult task, is key for developing a full understanding of climate change. Data-collection networks for the direct observation of climatic variables (such as precipitation, temperature, 

and stream and lake stage) have, in general, been in existence 

for fewer than 200 years. This information is vital for identifying current trends, but the period for which direct observations 

are available is quite short relative to the millions of years 

over which climate has been changing. Current understanding of past climates has been developed largely on the basis 

of indirect observations of fossils (Betancourt and others, 

2000); geochemistry (Winograd and others, 1988); chemistry 

of ice cores, soils, and lake sediments (Petit and others, 1999); 

and tree rings (Gray and others, 2004). Predictions of future 

climate trends are generated by highly sophisticated global circulation models (Intergovernmental Panel on Climate Change, 

2013). Different models generally predict similar trends, but 

there are important differences among predictions. 

Reducing the uncertainty in our knowledge of past, 

current, and future climates is an important goal of earth 

science research. Improved techniques for reconstructing past 

climates, both in terms of means and variations of climatic 

variables, can reduce uncertainty and help guide adaptation and mitigation activities (Brekke and others, 2009). 

Continued monitoring will help to determine to what extent 

recent climatic patterns are a part of either long-term trends 

or short-term natural variability; this information can also 

provide some insight on the role of energy development in 

climate change. Improved methods for measuring and estimating precipitation, temperature, streamflow, and other variables 

may involve combining traditional approaches with data collected remotely from land-based and satellite-based systems. 

Enhanced data collection will also allow for better calibration 

of global circulation models, which could potentially lead to 

reductions in uncertainties in predictions of climate trends for 

coming decades and centuries. 

Figure 39. Predicted temperature change, in degrees Celsius, for western North America for June–August for the period 2081–2100 

relative to average temperature for 1986–2005 (25th, 50th, and 75th percentile of distribution of CMIP5 ensemble model predictions for 

the RCP4.5 scenario). (Intergovernmental Panel on Climate Change, 2013)

EXPLANATION

0.5 1 1.5 2 3 4

Temperature change, in degrees Celsius (°C)

25% 50% 75%
Science for Addressing the Water-Energy Nexus 85

Monitoring water and ecosystem resources over extended 

periods of time is crucial for identifying and understanding 

hydrologic and ecological trends and links to climatic trends 

(Brekke and others, 2009). The value of monitoring networks is addressed in an earlier section, but it is important to 

emphasize the role of resource monitoring in developing an 

understanding of climate change and its effects on natural and 

human-affected systems. Studies on how ecosystems adapted 

to changes in climate in the past can provide insight into how 

they may be affected in the future. In particular, ecosystems 

and species most vulnerable to the adverse effects of climate 

change can be identified, and studies can be conducted to 

determine how those vulnerabilities can be reduced. 

The development of enhanced analytical techniques for 

characterizing floods, droughts, and other extreme hydrologic 

events can improve our understanding of the natural occurrence and variability of these events and support efforts to 

mitigate their effects. This work would involve studying the 

occurrence and severity of historical events and developing 

improved methods for analyzing the magnitude and frequency 

of past and recent floods, droughts, and rises in sea level. The 

adverse effects from high-intensity hydrologic events in the 

future can be reduced if maps of regions that will be vulnerable to these events can be produced. These maps would also 

benefit energy developers when planning future energy operations and infrastructure. 

Carbon dioxide concentrations in the atmosphere are at 

their highest levels in at least the past 800,000 years (Luethi 

and others, 2008; Hönisch and others, 2009; Pagani and 

others, 2010). Developing a fundamental understanding of 

the role that carbon plays in climate change is an important 

research objective. Research focused on the interactions of 

natural carbon storage and exchange, climate, land use, and 

biogeochemical processes at all scales, from plot to global, is 

particularly useful. Also important are assessments of carbon 

storage in and exchange among ecosystems, geologic formations, water bodies, and the atmosphere. Earth science research 

relevant to geologic carbon sequestration (see Box K—Carbon 

Capture and Sequestration) includes assessing subsurface CO2

storage capacities in geologic units; monitoring water levels, 

water quality, and seismic activity; and conducting intensive small-scale studies to gain a fuller understanding of the 

physical, geochemical, and biologic effects of the subsurface 

injection of CO2

. Monitoring freshwater aquifers is important 

to ensure the early detection of contaminants related to carbon 

sequestration. Tools for predicting where, when, and how 

injection operations induce earthquakes would benefit society 

greatly, as would innovations that could reduce the number 

and severity of these earthquakes.

Byproducts and Waste Streams of Energy 

Development

The Earth sciences provide a foundation for addressing 

issues associated with the broad spectrum of byproducts and 

waste streams related to energy production and use. An assessment of the quantities and physical, chemical, and biological 

characteristics of waste material is a requisite first step in 

evaluating alternative options for disposition of the material, 

options that include treatment, surface discharge, subsurface 

discharge, and beneficial use or reuse. Equally important is 

research on the direct and indirect effects of energy waste 

streams on water and ecosystem resources at local, regional, 

and national scales. Detailed chemical and isotopic characterization can help to identify sources of contaminants in 

freshwater systems and can provide insight into the processes 

that control contaminant movement. The identification of environmentally sound reuses or alternative means for disposition 

of byproducts such as produced water and carbon combustion 

residues has tangible benefits—it would reduce the requirements for freshwater and the need for waste disposal.

Atmospheric emissions of greenhouse gases, other gases, 

and particulates raise concerns regarding climate change and 

the impairment of water quality by acid deposition, mercury, 

and other contaminants (see Box J—Energy, Atmospheric 

Priorities for Studying Energy Byproducts 

and Waste

• Quantify and characterize waste streams.

• Determine the fate of waste streams and their effects 

on water and ecosystem resources.

• Identify alternative uses or means of disposition for 

wastes.

Climate change has affected habitat for many wildlife species.
86 The Water-Energy Nexus—An Earth Science Perspective

Emissions, and Water Quality). Carbon dioxide is an important atmospheric greenhouse gas; coal-fired power plants and 

motor vehicles are the two largest sources of carbon dioxide 

emissions, respectively. Substantial amounts of methane, 

another potent greenhouse gas, can also be emitted by oil and 

natural gas wells and distribution systems. Sulfur dioxide, 

nitrogen, and mercury emissions from coal-fired plants and 

other sources can affect water quality. The U.S. Environmental 

Protection Agency, responsible for regulating and monitoring atmospheric emissions in the United States, publishes 

annual estimates of emissions for the major greenhouse gases 

(U.S. Environmental Protection Agency, 2013b). 

The acidity of precipitation (and dry deposition) and the 

geographic distribution of it across the United States can only 

be determined with a dispersed network of collection sites. 

The National Atmospheric Deposition Program maintains the 

largest such network in the United States. Initiated in 1977, 

the program supports a network of sites where precipitation 

is collected weekly; data on acidity and other constituents are 

available for no cost (http://nadp.sws.uiuc.edu/NADP/). Data 

from networks such as this were instrumental in documenting 

the extent and severity of acid rain in the 1970s and 1980s; 

they remain important in tracking trends over time. Results of 

extensive research programs identified the deleterious effects 

of acid rain and associated contaminants on ecosystems, soils, 

water, and vegetation (Likens, 2011). From the 1980s to the 

present, data collection and research have provided a basis for 

revised regulations and policy; these revisions have resulted 

in substantial reductions in annual atmospheric deposition rates of sulfate (http://nadp.sws.uiuc.edu/maplib/ani/

so4_dep_ani.pdf) and nitrate (http://nadp.sws.uiuc.edu/maplib/

ani/no3_dep_ani.pdf) in the United States. Continued resource 

monitoring and research can enhance our understanding of the 

effects of atmospheric deposition of contaminants in a number 

of ways, for example, by identifying factors that promote 

or retard the transport of pollutants such as mercury within 

hydrologic and biologic systems.

In addition to atmospheric emissions, thermoelectric 

power plants could have additional byproducts of concern, depending on cooling system design and fuel type. 

Once-through cooling systems can result in high heat loads to 

the streams or lakes that provide the cooling water. The resulting increased temperature in the water body can have adverse 

effects on aquatic ecosystems; these effects are compounded 

during times of drought when the ecosystems are already 

under stress (Electric Power Research Institute, 2012). Coal 

combustion products (coal ash) can be used in a number of 

beneficial ways, but recent research has raised concerns on 

the environmental impacts of its reuse and disposal (Pandey 

and Singh, 2010; Ruhl and others, 2012). Annual production 

amounts of coal ash are published by the American Coal Ash 

Association (American Coal Ash Association, 2014), but there 

is no available data base on the chemistry of coal ashes. The 

U.S. Environmental Protection Agency has recently issued 

new regulations for the disposition of coal ash (U.S. Environmental Protection Agency, 2014a).

Produced water is the largest byproduct (by volume) of 

oil and natural gas production. Rates of extraction and chemical characteristics of produced waters vary with location, and 

these variations have important implications on management, 

use, and potential environmental impacts of the water. Information on volumes and quality of produced waters is important for identifying potential beneficial uses. The information 

also can be used to assess saline resources, identify sources of 

saline water suitable for operations such as hydraulic fracturing, determine the feasibility of wastewater injection operations, and further research on geologic carbon sequestration. 

Unfortunately, there is no system in place for tracking rates 

of produced-water extraction at the national level. A database 

on water-quality characteristics of produced waters from most 

basins in the United States is maintained by the U.S. Geological Survey (http://energy.cr.usgs.gov/prov/prodwat/data.htm). 

Information contained in that database includes well location 

and depth, geologic formation, and concentrations of major 

and minor ions, organic compounds, radionuclides, and chemical isotopes. Along with other uses, this water-quality information potentially could be used to determine the age and origin 

of water in saline aquifers, which in turn could provide insight 

on hydraulic connections to freshwater reservoirs. 

Abandoned coal and uranium mine lands are the main 

source of acid mine drainage. Under the leadership of the 

Bureau of Land Management, a number of Federal agencies 

have collaborated to create the Abandoned Mine Lands Portal 

(http://www.abandonedmines.gov/index.html), which provides 

information on types and locations of abandoned sites and 

the environmental, health, and safety concerns associated 

with each site. Most abandoned coal mines are in the eastern 

United States (primarily West Virginia, Pennsylvania, and 

Kentucky), whereas most abandoned uranium mine lands are 

Oilfield waste arrives by tanker truck at a wastewater disposal 

facility near Platteville, Colorado. After removal of solids and oil, 

the wastewater is injected into a deep well for permanent storage 

underground.
0 200 400 METERS

0 600 1,200 Feet

N

Science for Addressing the Water-Energy Nexus 87

located in 14 western states. Acid mine drainage can occur for 

more than 100 years after a site has been abandoned. Research 

has already shown how acidic waters are created from minewaste piles and how acidification of groundwater and streams 

can impair ecosystems (for example, Nordstrom and Alpers, 

1999). Remediation of abandoned sites is expensive, and progress on remediation is hindered by limited funding. Research 

can provide a better understanding of the physical, geochemical, and biological processes that contribute to the natural 

attenuation of contaminants from acid mine drainage. Also 

important is the development of tools for evaluating alternative approaches for reducing the adverse effects of acid mine 

drainage on streams (Walton-Day and others, 2012; Runkel 

and others, 2012). Advances in research could lead to more 

cost-effective methods for site remediation.

The many thousands of abandoned, unsealed wells that 

are present in mature oil and gas fields across the United 

States present an important legacy issue to consider. Most 

States have records showing locations for wells that were 

abandoned in the most recent decades, but available funding 

for sealing these wells is not always sufficient to cover the 

task. More problematic are wells that were abandoned in the 

late 1800s and early and middle decades of the 1900s; records 

of these wells are largely nonexistent, and locating these wells 

can be extremely difficult. Aerial geophysics is one area of 

research that has proved to be useful in locating abandoned 

wells (fig. 40).

Priorities for Studying the Effects of New 

Technologies

• Improve our understanding of hydraulic fracturing.

• Assess hydrologic and environmental impacts of 

emerging technologies.

Figure 40. False color map showing the response from 

helicopter electromagnetic surveys for a portion of the Salt 

Creek oilfield near Casper, Wyoming. Warmer colors indicate 

the presence of highly conductive materials, in this case steel 

casings from abandoned oil wells. This image is a reminder of the 

remnants of legacy oil and gas operations in many portions of the 

United States. (Image courtesy of Richard Hammack, National 

Energy Technology Laboratory, Pittsburgh, Pennsylvania)

Contamination of groundwater and surface water by 

nutrients contained in fertilizers has long been a concern in the 

midwestern United States (Gilliom and others, 2006). Because 

much of the corn and soybeans grown in the United States is 

used as biofuel feedstocks, some of the contamination can be 

attributed to energy production. Our knowledge of the extent 

of nutrient contamination, the mechanisms by which nutrients and other agricultural chemicals are transported, and the 

effects of the contamination on ecosystems has been obtained 

through programs for monitoring water quality and ecosystem 

health and by large-scale research efforts. As an example, 

recent research has shown that between 2006 and 2011, 

approximately 530,000 hectares of native grass lands in the 

western corn belt of the United States were converted to row 

crops, primarily corn and soybeans (Wright and Wimberly, 

2013). The primary driving force for this large-scale conversion is the historically high grain prices, which have been 

created in large part by the demand for biofuel feedstocks. 

Continued monitoring and additional research can help in 

developing a clear understanding of the effects that land conversion and other agricultural operations have on water quality 

and ecosystems and in identifying potential improvements in 

farming practices.

Emerging Energy Development Technologies

Technology is continually evolving. Evaluating the 

viability and hydrological and environmental impacts of new 

energy development technologies is an important but challenging task for the earth sciences. Once an energy-development 

technique is found to be effective and economical, it might 

be implemented on a widespread basis before researchers and 

regulators can identify and analyze all the associated effects. 

Carefully designed data-collection networks and directed 

research can improve our understanding of these technologies 

and provide useful information to resource managers, energy 

developers, and the general public.

Recent advancements in technology for extracting 

hydrocarbon fuels have left large gaps in our understanding 

of effects associated with the application of these technologies. The rapid expansion in use of hydraulic fracturing (see 

Box E—Hydraulic Fracturing) combined with directional 
88 The Water-Energy Nexus—An Earth Science Perspective

drilling has raised concerns in regard to water quality—specifically, the possible subsurface migration of methane and saline 

fluids to freshwater supplies and the disposition of produced 

waters. Groundwater-quality monitoring is useful for detecting 

subsurface migration of saline fluids. Data obtained from laboratory experiments and intensive, site-specific field monitoring 

can improve our understanding of the nature of the fractures 

created by hydraulic fracturing, in terms of density, aperture, 

connectivity, and vertical and horizontal extent. These data can 

also provide insight on fluid movement, chemical reactions, 

and seismic activity that could occur as a result of hydraulic 

fracturing and other operations. For example, fluids produced 

from some Marcellus Shale gas wells have very high salinities. Identifying the source of that salinity (naturally occurring brines or dissolution of reservoir minerals) can shed light 

on how hydraulic fracturing affects a reservoir. An approach 

looking at the relationships between the sodium, chloride, and 

bromide concentrations in produced water has been developed 

for differentiating between these sources (Engle and Rowan, 

2013).

New technologies hold great promise for solving important energy and water problems (U.S. Department of Energy, 

2014), but the water quantity and quality issues associated 

with these technologies are not always apparent. These 

technologies include, for example, geologic sequestration 

of carbon dioxide, enhanced geothermal systems, cellulosic 

bioethanol, and algal biodiesel. Research into the water-related 

needs and issues of new technologies can help to determine 

their viability in different regions. Each proposed technology 

has specific issues, but the core issues of freshwater availability, protection of water quality, and the availability and 

use of saline or wastewater form a common thread among all 

energy development technologies. Resource assessment and 

monitoring networks can provide information for evaluating 

the hydrological and environmental effects of new technologies on a broad scale, but more detailed data collection on 

a site-specific scale might be required. In addition, in-depth 

hydrogeological and geochemical characterizations on both 

regional and local scales will be necessary for operations such 

as geologic carbon sequestration and enhanced geothermal 

systems. As the use of new technologies ramps up, additional 

important research issues may unfold.

Energy Use for Water

Research plays an important role in efforts to minimize 

the energy intensity of the water-use cycle. Research in 

engineering fields provide perhaps the most obvious examples—research on more energy-efficient hot-water heaters and 

pumps or research on extracting energy from wastewater—but 

earth science research also has an important role to play. Earth 

science research can identify new water supplies, better characterize the quantity and quality of existing water supplies, 

suggest ways to avoid contamination of water supplies, and 

evaluate alternative approaches for remediating contaminated 

water.

In situations where local freshwater supplies are being 

depleted, local saline groundwater could be an attractive 

supplemental water source compared to more distant freshwater sources that might have a high energy cost associated 

with conveyance. Earth science research can answer questions about the quantity and quality of the saline groundwater 

resource, as well as how much water a saline aquifer can yield 

to wells. Such information is crucial to the planning process 

of water managers and engineers. Before construction began 

on El Paso’s desalination plant, hydrogeologic monitoring 

data and results from a groundwater-flow model were used to 

determine optimum locations for the plant and the pumping 

wells that feed it (Heywood and Yager, 2003; El Paso Water 

Utilities, 2007).

Managed aquifer recharge (MAR) is used to supplement 

groundwater supplies and has the potential to reduce overall 

energy use for delivering water to residential, agricultural, and 

industrial interests. The viability of MAR systems depends, 

among other factors, on the hydraulic and geochemical characteristics of the receiving aquifers. Research to better understand how exactly these characteristics influence the storage 

and recovery processes can lead to more efficient system 

operations. Developing methods to estimate these characteristics for different areas on the basis of existing information 

would facilitate the selection of appropriate areas for managed 

aquifer recharge.

Priorities

• Improve our understanding of managed aquifer 

recharge in different settings.

• Protect water quality and evaluate natural processes for remediating contaminated water.

Continued on page 90
Science for Addressing the Water-Energy Nexus 89

Saving Energy and Saving Water

Energy consumed for water represents an important 

part of the Nation’s energy demand, and that consumption 

is likely to increase in the future as population increases. 

Fortunately, current and future energy requirements could 

be reduced by saving water. Opportunities to save water exist at each stage of the water-use cycle. Reducing the leakage of water from conveyance structures, pumps in water 

and wastewater treatment plants, distribution pipelines, 

residential plumbing, and other components of the cycle 

represents one such opportunity. Water heating consumes 

more energy than any other part of the water-use cycle, so 

saving water at that stage could result in substantial energy 

savings. Using less cold water in indoor residential, commercial, and industrial applications, such as by installing 

low-flow toilets, would save the energy embedded at the 

early stages (water conveyance, treatment, and distribution) 

and at later stages (wastewater collection and treatment) of 

the water-use cycle. Using less water in outdoor residential, 

commercial, and industrial applications would also save 

the energy embedded at the early stages of the water-use 

cycle. And as has been stated several times, protecting the 

quality of water could save energy associated with some 

types of advanced water treatment that might be needed 

to remove contaminants from water. Finally, saving water 

has the added benefits of reducing the carbon footprint of 

the water-use cycle and allowing more water to remain in 

aquifers, streams, lakes, and other water bodies for environmental uses.

Although estimates of the actual amounts of water 

withdrawn and consumed in the United States for the 

development and use of energy are clouded with uncertainty, it is clear that energy-related water withdrawal and 

consumption can be reduced in several ways. Individuals, 

businesses, and government agencies can simply alter their 

use of the operations that consume energy, for example, 

turning off unused lights or lowering the setting on the 

home thermostat in winter. In addition, methods for developing energy that are less water intensive can be improved 

and expanded—generation of electricity by passive solar 

and wind methods consume negligible amounts of water. 

Development of more energy-efficient processes will also 

lead to a reduction of water withdrawal and consumption. 

For example, the U.S. Environmental Protection Agency 

finalized new fuel-economy standards for cars and light 

trucks in 2012 that call for an average fuel-economy of 

23 km/L (54.5 miles per gallon) by the year 2025 (U.S. Environmental Protection Agency, 2012a). It is estimated that 

the standards will reduce daily consumption of hydrocarbon fuels in the United States by about 350 million L/d. 

The reduced consumption of transportation fuels translates 

to a reduced amount of water needed to extract and process 

those fuels.
90 The Water-Energy Nexus—An Earth Science Perspective

Protecting water quality saves energy—clean water 

requires less treatment than contaminated water. Important 

water-quality issues that are being addressed through earth science research include the identification of sources of contaminants in water supplies, the explanation of temporal variability 

in contaminant concentrations, and the development of an 

understanding of why and where natural attenuation processes 

can remove contaminants from water supplies. For example, 

research done in the vicinity of a public-supply well owned by 

the City of Modesto, California, was instrumental in determining the source of nitrate and uranium in the well water 

and identifying well-operation practices that could minimize 

the contamination (Jurgens and others, 2008). In Lincoln, 

Nebraska, research explained why and when concentrations of 

the pesticide atrazine were changing over time in water from 

the city’s municipal wells (Carr, 1993; Verstraeten and others, 

1999). Such information could be used by water utilities to 

better manage their treatment process during periods of high 

contaminant levels either by reducing the intake of water or by 

blending it with cleaner water. Other studies have explained 

why natural attenuation processes are effective in protecting 

water supplies in some locations but not in others (for example, McMahon and others, 2008; Bradley and Chapelle, 2010). 

Information like this could be used to select new locations 

for water wells or water intakes to take advantage of natural 

attenuation processes. Earth science research can also assist in 

evaluating various alternatives for the disposition of byproducts of wastewater treatment processes. Operations such as the 

land application of biosolids and the use of treated wastewater 

for managed aquifer recharge projects may be energy and 

water efficient, but only if the quality of existing water supplies are not degraded. 

Conclusions

Two important challenges facing the United States are 

preserving sustainable supplies of freshwater for humans and 

ecosystems and ensuring adequate sources of energy for future 

generations. These challenges need not be viewed as mutually exclusive options, even though competition for limited 

water and energy resources already is occurring in some 

parts of the country. Conflicts can be avoided and water and 

energy resources can be protected with prudent management 

strategies. The material presented in this report is intended 

to provide resource managers and the general public with an 

enhanced appreciation of the complex ways in which water 

and energy are interconnected.

Future development of water and energy resources 

within the United States will be guided by policy decisions 

at local, State, and national levels. Considerations such as 

population trends, public opinion, the economy, and technology factor into water and energy policies; however, the 

foundation needed for informed policy decisions is provided 

by earth science data collection and research. The role of 

science is to identify and analyze important technical issues, 

to describe potential solutions to relevant problems, and to 

support informed decision making by communicating findings to resource managers, energy producers, and the public. 

Science improves our understanding of key processes, such as 

the chemical, physical, and biological reactions occurring in 

a reservoir during hydraulic fracturing. Science also provides 

a platform for identifying potential environmental or human 

health ramifications of energy development. To remain relevant, earth science data-collection and research efforts must 

continue to evolve as new development technologies emerge. 

Current understanding of the water-energy nexus is 

limited by uncertainty in our knowledge of important issues, 

such as the amount of freshwater that is available and the 

amount of water that is used in energy development. Predictions of future water and energy needs and availability can be 

improved if this uncertainty can be reduced. Water and energy 

resource management efforts are also complicated by the fact 

that policy makers, resource managers, and water and energy 

developers are often faced with a series of tradeoffs in their 

decisions. One example is balancing the cost of added water 

requirements and potential water-quality issues against the 

benefit of reduced atmospheric emissions of greenhouse gases 

at coal-fired power plants by adopting carbon capture and 

geologic sequestration strategies. Earth science data collection 

and research can help to elucidate the benefits and pitfalls of 

tradeoff options. 

Advances in technology might eventually alleviate some 

of the competition associated with water and energy development. Adoption of new technologies can result in considerable 

deviations between actual and predicted trends. Consider, for 

example, the effects of recent developments in directional 

drilling and hydraulic fracturing on estimates of natural gas 

reserves in the United States. In 1993, the Energy Information 

Administration estimated natural gas reserves in the United 

States at about 5 trillion m3

. Seventeen years later (2010), 

those estimates had increased to 9 trillion m3

, largely because 

these new technologies allow recovery of gas that was previously believed to be inaccessible. Technologies such as algal 

biodiesel, bioethanol from second-generation feedstocks, and 

enhanced geothermal systems hold great promise, but the 

economic viability of these technologies has yet to be demonstrated at commercial scales, and their water requirements 

are largely unknown. In planning for future water and energy 

needs, policy makers may be drawn by the allure of promising, 

but not fully developed, technologies to address pressing water 

and energy concerns. A more pragmatic approach for water 

and energy policy planners is to seek solutions to our problems solely on the basis of existing technology. Technology 

will continue to evolve in the future, and new advances will 

no doubt contribute to our understanding of and our ability to 

address the important water-energy issues that we face as a 

Nation. Prudent resource-management strategies will be able 

to incorporate new advances as they become available.
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Wyoming Oil and Gas Conservation Commission, 2014, Water 

production, Powder River Basin: Wyoming Oil and Gas 

Conservation Commission, accessed October 31, 2014, at 

http://wogcc.state.wy.us. 

Zogorski, J.S., Carter, J.M., Ivahnenko, Tamara, Lapham, 

W.W., Moran, M.J., Rowe, B.L., Squillace, P.J., and Toccalino, P.L., 2006, The quality of our Nation’s waters—

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Circular 1292, 101 p. (Also available at http://pubs.usgs.

gov/circ/circ1292.)
106 The Water-Energy Nexus—An Earth Science Perspective

Photograph Credits

Page 1. Mallik gas hydrate production test research project, 2002. Photograph by 

U.S. Geological Survey (USGS).

Page 2. Livestock well with solar-powered pump. Photograph by Audrey Plenty Hoops.

Page 3. Dam and reservoir. Photograph by USGS. 

Page 4. Table lamp. Photograph by Richard Healy, USGS.

Page 5. Top: Coal mining operation (photograph by Bureau of Land Management). Center: 

Water impoundment (photograph by Bill Cunningham, USGS). Bottom: Fossil fuel extraction 

(photograph by Bureau of Land Management). 

Page 6. Figure 1, left column, top to bottom: Wind farm (photograph by Don Becker, USGS); oil 

pumper (photograph by Bureau of Land Management); corn (photograph by Cheryl Eddy-Miller, 

USGS). Right column photographs ©2002 Corel Corporation.

Page 12. Demonstrators rallying against fracking. Photograph by Albany Times Union, used with 

permission.

Page 14. Bakken drilling and completion activities. Photograph by David Ferderer, USGS.

Page 17. Glass of water and salt. Photograph by USGS.

Page 20. Smog over downtown Los Angeles, California. Photograph by Massimo Catarinella; 

Creative Commons Attribution-ShareAlike 3.0 Unported (http://creativecommons.org/licenses/

by-sa/3.0/legalcode)

Page 23. Left: Alfalfa field (photograph by Bruce Engle). Right: Pilot-scale constructed wetland 

water-treatment system (photograph courtesy of James Castle and John Rogers, Jr., Clemson 

University).

Page 24. Mountaintop coal removal mine. Photograph by Calin Tatu, USGS.

Page 29. Left column: former site of Saunders, West Virginia (photograph from Davies and 

others, 1972). Right column: Acid mine drainage (photograph from Christensen, 2005).

Page 31. Uranium mine and tailings, Emery County, Utah. Photograph courtesy of Emery County 

Travel Bureau.

Page 32. Miscanthus sinensis. Photograph by Georges Jansoone.

Page 38. Browns Ferry nuclear power station. Photograph by U.S. Nuclear Regulatory 

Commission.

Page 40. Palo Verde Nuclear Generating Station. Photograph by U.S. Nuclear Regulatory 

Commission.

Page 41. The Geysers geothermal field in northern California. Photograph by Julie DonnellyNelson, USGS.
Photograph Credits 107

Page 42. Ivanpah Solar Electric Generating System in the Mojave Desert of California. 

Photograph by NRG Energy, Inc., used with permission.

Page 43. Coal ash spill in Kingston, Tennessee. Photograph by the Tennessee Valley Authority.

Page 47. Upper: Yucca Mountain crest (photograph by U.S. Department of Energy). Lower: 

Ethanol plant (photograph by Kathleen Neitzert, USGS).

Page 48. Hoover Dam. Photograph by U.S. Bureau of Reclamation.

Page 52. Cornfield. Photograph by Cheryl Eddy-Miller, USGS.

Page 55. Electrical transmission lines. Photograph by Robert and Mihaela Vicol, 

publicphoto.org.

Page 57. Left: pumping groundwater (photograph by Bruce Campbell, USGS). Right: Moving 

surface water (photograph by USGS Utah Water Science Center).

Page 58. Edmonston Pumping Plant. Photograph by California Department of Water Resources.

Page 59. Lake Mead. Photograph by U.S. Bureau of Reclamation.

Page 62. Otay Water Treatment Plant solar photovoltaic energy system. Photograph courtesy 

of the City of San Diego Public Utilities Department and SunEdison.

Page 63. Bottled water. Photograph by Richard Healy, USGS.

Page 64. Hot tub. Photograph Echo Bay Resort and Spa; Creative Commons AttributionNonCommercial 2.0 Generic (http://creativecommons.org/licenses/by-nc/2.0/legalcode).

Page 66. California wastewater recycling Facility. Photograph by U.S. Environmental Protection 

Agency.

Page 68. Demonstration wetland. Photograph by Joan S. Daniels, USGS.

Page 69. Spring-fed stream. Photograph by Joe Giersch, USGS.

Page 71. Above: Streamgage on the White River. Right: Flaring of natural gas. Photographs by 

USGS.

Page 76. Seminoe Dam and power plant. Photograph by Jon Mason, USGS.

Page 77. Desert spring. Photograph by Richard Healy, USGS.

Page 80. State capital building in Boise, Idaho. Photograph by Jon Sullivan.

Page 82. Groundwater methane measurement. Photograph by USGS.

Page 85. A polar bear on Arctic Ocean ice August 23, 2009. Photograph by Patrick Kelley, 

U.S. Coast Guard.

Page 86. Oilfield waste. Photograph by William Ellsworth, USGS.

Page 89. Mountain stream in Grand Teton National Park. Photograph by Melanie Clark, USGS.
Publishing support provided by:

Denver and Rolla Publishing Service Centers 

For more information concerning this publication, contact: 

Chief, National Research Program, Central Branch 

U.S. Geological Survey 

Box 25046, Mail Stop 418 

Denver, CO 80225 

Or visit the National Research Program Web site at: 

http://water.usgs.gov/nrp/

Healy and others—The Water-Energy Nexus—An Earth Science Perspective—Circular 1407

ISSN 1067-084X (print)

ISSN 2330-5703 (online)

http://dx.doi.org/10.3133/cir1407