U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2014–5184

A product of the USGS National Water Census and the 

USGS National Streamflow Information Program

Withdrawal and Consumption of Water by Thermoelectric 

Power Plants in the United States, 2010
Cover photograph. Steam rising from the once-through cooling reservoir of the coal-fired 

Mount Storm Power Station in Grant County, West Virginia, owned by Dominion Resources, Inc. 

Photograph by Raeky [Public Domain], via Wikimedia Commons.
Withdrawal and Consumption of Water 

by Thermoelectric Power Plants in the 

United States, 2010

By Timothy H. Diehl and Melissa A. Harris

A product of the USGS National Water Census and the

USGS National Streamflow Information Program

Scientific Investigations Report 2014–5184

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2014

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

Suggested citation:

Diehl, T.H., and Harris, M.A., 2014, Withdrawal and consumption of water by thermoelectric power plants in 

the United States, 2010: U.S. Geological Survey Scientific Investigations Report 2014–5184, 28 p., http://dx.doi.

org/10.3133/sir20145184.

ISBN 978-1-4113-3851-7

ISSN 2328-0328 (online)

ISSN 2328-031X (print)
iii

Contents

Abstract ..........................................................................................................................................................1

Introduction.....................................................................................................................................................1

Purpose and Scope ..............................................................................................................................2

Acknowledgments................................................................................................................................2

Methods...........................................................................................................................................................2

Identification of Plants for Model Development and Water-Use Estimation..............................2

Compilation of Descriptive and Operational Data...........................................................................4

Plant Characteristics...................................................................................................................4

Heat- and Water-Budget Data...................................................................................................4

Classification of Plants ........................................................................................................................4

Generation and Cooling-System Type......................................................................................4

Classification of Cooling Ponds.................................................................................................5

Water Sources and Water Types ..............................................................................................8

Models for Estimating Thermoelectric Water Use..........................................................................8

Consumption.................................................................................................................................8

Withdrawal....................................................................................................................................9

Once-Through Cooling System Withdrawals.................................................................9

Recirculating Pond Withdrawals ...................................................................................12

Tower Withdrawals ..........................................................................................................12

Complex Plant Withdrawals............................................................................................12

Development of Consumption and Withdrawal Coefficients .............................................12

Results and Discussion...............................................................................................................................13

Estimated Thermoelectric Water Use for 2010 ..............................................................................13

Consumption and Withdrawal Coefficients....................................................................................13

EIA-Reported Water Use in 2005 and 2010 .....................................................................................13

Alternative Water................................................................................................................................17

Comparison of EIA 2010 Data to USGS Model Results.................................................................19

Conclusions...................................................................................................................................................20

Selected References...................................................................................................................................21

Glossary.........................................................................................................................................................27

Appendix 1. Estimated and Reported Water Withdrawals and 

Consumption for 1,290 Thermoelectric Plants in the 

United States, 2010 (Excel file) ......................................http://pubs.usgs.gov/sir/2014/5184/
iv

Figures

1. Map showing geographic distribution of the 1,290 thermoelectric power plants 

modeled to estimate water withdrawal and consumption in the United States, 2010......3

2–7. Graphs showing—

 2. Classifications of 32 plants at 28 once-through or recirculating cooling 

ponds for which water budgets were developed, including the watershed 

runoff threshold determining pond cooling category, for thermoelectric 

power plants in the United States ......................................................................................7

 3. Selected reported condenser ranges and corresponding intake water 

temperatures for 128 thermoelectric power plants in the United States...................10

 4. Median, minimum, and maximum estimated condenser ranges and reported 

condenser ranges for thermoelectric power plants in the United States .................11

 5. Water withdrawal by generation type and cooling-system type for 

simple thermoelectric power plants, 2005 and 2010.................................................... 16

 6. Net electrical generation by generation type and cooling-system type 

for simple thermoelectric power plants, 2005 and 2010 ............................................. 16

 7. Water consumption by generation type and cooling-system type for 

simple thermoelectric power plants, 2005 and 2010......................................................17

8. Pie charts showing alternative water withdrawals by thermoelectric plants in 

the United States as reported to the U.S. Department of Energy, Energy 

Information Administration, and estimated by the U.S. Geological Survey, 2010............18

9. Pie charts showing alternative water consumption by thermoelectric plants in 

the United States as reported to the U.S. Department of Energy, Energy 

Information Administration, and estimated by the U.S. Geological Survey, 2010............18

Tables

1. Classification for condenser duty estimation method by generation type 

for thermoelectric plants in the United States.........................................................................4

2. Classification for modeling approach to consumption and withdrawal by 

cooling-system type for thermoelectric plants in the United States ...................................5

3. Net electrical generation for water-using thermoelectric plants according to 

generation type and cooling-system type as reported to the U.S. Department of 

Energy, Energy Information Administration for 685 plants for 2005, 835 plants for 

2010, and 1,290 plants for 2010 as analyzed by the U.S. Geological Survey .......................6

4. Cooling water source codes and descriptions........................................................................8

5. Cooling water type codes and descriptions.............................................................................8

6. Thermoelectric plant water withdrawals by generation and cooling-system types 

as reported to the U.S. Department of Energy, Energy Information Administration 

for 2005 and 2010, and as modeled by the U.S. Geological Survey for 2010 .....................14

7. Thermoelectric plant water consumption by generation and cooling-system types 

as reported to the U.S. Department of Energy, Energy Information Administration 

for 2005 and 2010, and as modeled by the U.S. Geological Survey for 2010 .....................14

8. Thermoelectric water-withdrawal coefficients calculated from flow rates and 

net electrical generation as reported to the U.S. Department of Energy, Energy 

Information Administration and as calculated from modeled estimates by the 

U.S. Geological Survey for 2010 ...............................................................................................15

9. Thermoelectric water-consumption coefficients calculated from flow rates 

and net electrical generation as reported to the U.S. Department of Energy, 

Energy Information Administration and as calculated from modeled 

estimates by the U.S. Geological Survey for 2010.................................................................15
v

Conversion Factors and Datum

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm) 

inch (in.) 25.4 millimeter (mm)

mile (mi) 1.609 kilometer (km)

Volume

gallon (gal) 3.785 liter (L) 

gallon (gal) 0.1337 cubic foot (ft3) 

cubic foot (ft3) 0.02832 cubic meter (m3)

Concentration

milligrams per liter (mg/L) 0.058418 grains per gallon (gr/gal) (U.S.)

Pressure

atmosphere (atm) 101.3 kilopascal (kPa)

Energy

British thermal unit (Btu) 1,055.06 joule (J)

British thermal unit (Btu) 252.16 calorie (cal)

British thermal unit (Btu) 0.0002931 kilowatt hour (kWh)

gigawatt hour (GWh) 3.412 × 109 British thermal unit (Btu)

kilowatt hour (kWh) 3.6 × 106 joule (J)

kilowatt hour (kWh) 3,412 British thermal unit (Btu)

megawatt (MW) 1 × 106 joule per second (J/s)

megawatt (MW) 8.6042 × 108 calories per hour (cal/h)

megawatt hour (MWh) 3.6 × 109 joule (J)

megawatt hour (MWh) 3.412 × 106 British thermal unit (Btu)

Rate

gallon per kilowatt hour (gal/kWh) 1.0515 × 10–6 liter per joule (L/J)

gallon per kilowatt hour (gal/kWh) 4.3995 × 10–6 liter per calorie (L/cal)

gallon per megawatt hour (gal/MWh) 1.0515 × 10–9 liter per joule (L/J)

gallon per megawatt hour (gal/MWh) 4.3995 × 10–9 liter per calorie (L/cal)

gallon per million British thermal units 

(gal/MMBtu) 

3.412 gallon per megawatt hour (gal/MWh)

gallon per million British thermal units 

(gal/MMBtu)

3.5879 × 109 liter per joule (L/J)

billion gallons per day (Bgal/d) 43.813 cubic meter per second (m3/s)

million gallons per day (Mgal/d) 4.3813 × 10–2 cubic meter per second (m3/s)

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

°C= (°F–32)/1.8

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Concentrations of chemical constituents in water are given in milligrams per liter (mg/L).
vi

Selected Acronyms and Abbreviations

EIA U.S. Department of Energy, Energy Information Administration

EPA U.S. Environmental Protection Agency

FAO Food and Agriculture Organization

FGD flue-gas desulfurization

GAO U.S. Government Accountability Office

GWh gigawatt hour

MMBtu million British thermal units

NCDC National Climatic Data Center

NETL National Energy Technology Laboratory

NGCC natural gas combined cycle

NOAA National Oceanic and Atmospheric Administration 

QCLCD Quality Controlled Local Climatological Data

SSURGO Soils Survey Geographic (database)

USGS U.S. Geological Survey
Abstract 

Estimates of water use at thermoelectric plants were 

developed by the U.S. Geological Survey based on linked 

heat and water budgets, and complement reported thermoelectric water withdrawals and consumption. The heat- and 

water-budget models produced withdrawal and consumption 

estimates, including thermodynamically plausible ranges of 

minimum and maximum withdrawal and consumption, for 

1,290 water-using plants in the United States for 2010. Total 

estimated withdrawal for 2010 was about 129 billion gallons 

per day (Bgal/d), and total estimated consumption was about 

3.5 Bgal/d. In contrast, total withdrawal reported by the U.S. 

Department of Energy, Energy Information Administration 

(EIA), was about 24 percent higher than the modeled estimates, and total EIA-reported consumption was about 8 percent lower. Most thermoelectric generation in 2010 was not 

associated with thermodynamically plausible EIA-reported 

values of both withdrawal and consumption. 

An analysis of 2005 and 2010 EIA-reported water use 

indicated that withdrawal and consumption declined 18 percent and 34 percent, respectively. Alternative water types 

(types other than freshwater) accounted for approximately 

25 percent of all withdrawals in 2010, most of which occurred 

at plants with once-through cooling systems using saline and 

brackish tidal waters. Differences among withdrawal and 

consumption coefficients based on EIA-reported water use for 

2005 and 2010 and heat-budget model results for 2010 reveal 

opportunities for improving consistency and accuracy of 

reporting of water-use information at the plant scale.

Introduction

Water withdrawal and consumption at thermoelectric 

power plants represent an important but poorly quantified 

component of water use in the United States. Thermoelectric 

water withdrawals in 2005 were estimated at about 200 billion 

gallons per day (Bgal/d) and represented the largest single 

category of water withdrawals nationwide for that year (Kenny 

and others, 2009). In contrast, thermoelectric consumption was 

estimated to be only about 3 percent of national freshwater 

consumption in 1995 (Solley and others, 1998) and owing 

to uncertainties in reported information, the U.S. Geological 

Survey (USGS) suspended publication of thermoelectric 

consumption in its 2000 and 2005 water-use compilations 

(Hutson and others, 2004; Kenny and others, 2009). Uncertainties in estimates of thermoelectric water withdrawal1

and consumption reflect numerous factors, including contradictory definitions among different organizations, inconsistency in applying definitions, and data-quality problems 

and incompleteness in key databases (Diehl, 2011; Diehl and 

others, 2013). While published coefficients associating water 

consumption with power generation might be used to estimate 

national water consumption by thermoelectric power plants, 

available coefficients vary widely (Macknick and others, 2011) 

and fail to provide additional certainty in estimates. Given 

these difficulties, the National Research Council (2002) supported the USGS decision to suspend publication while noting 

a national interest in addressing the “financial and institutional 

pressures” that drove it.

As the Nation’s demand for water and energy continue to 

increase, there is growing awareness of the need for reliable estimates of withdrawal and consumption of water at thermoelectric 

plants (Murkowski, 2014). This awareness was expressed in a 

report by the U.S. Government Accountability Office (GAO) 

(2009), which recommended that the USGS resume reporting 

consumptive water use by thermoelectric power generation in 

the United States. In addition, the GAO (2009) report emphasized the need to begin tracking thermoelectric use of alternative water sources such as treated wastewater.

In 2010, the USGS responded to the GAO recommendation by initiating a program to improve the accuracy and 

precision of thermoelectric water withdrawal and consumption information. As part of this effort, Diehl and others 

(2013) developed a method to constrain and validate waterconsumption estimates by comparing them to linked heat and 

water budgets based on fuel use and electrical generation, 

which generally are tracked at power plants. Based on this 

information, the difference between reported energy input 

and output from each plant provides an approximation of the 

total energy available to consume water by evaporation. When 

further adjusted for the particular performance of each plant’s 

cooling and electrical generation system, the result is a reasonable constraint on what is physically possible in terms of water 

consumption at each plant. 

1

 Words and phrases shown in bold are listed in the Glossary.

Withdrawal and Consumption of Water by Thermoelectric 

Power Plants in the United States, 2010

By Timothy H. Diehl and Melissa A. Harris
2 Withdrawal and Consumption of Water by Thermoelectric Power Plants in the United States, 2010

Diehl and others (2013) describe the rationale and computational details for the application of linked heat- and waterbudget models to estimate water consumption at thermoelectric 

power plants of various configurations based on generator, 

boiler, and cooling-system type. They did not include estimates of consumption, nor did they address water withdrawal, 

which may be in principle constrained by similar thermodynamic assumptions. Water-use withdrawals are reported by 

the USGS as a removal from a natural source. Some power 

plants recirculate water from small ponds that are periodically replenished from other sources. Other plants draw water 

from ponds of similar size that receive sufficient runoff from 

their watersheds to eliminate the need for artificial replenishment; such ponds typically discharge to other bodies of water. 

Because the size of a pond does not determine its relation to 

the natural hydrologic system, distinguishing once-through 

withdrawals from recirculated pumpage requires a more complex analysis that has not been addressed in earlier work. 

Purpose and Scope

This report builds on the work reported by Diehl and 

others (2013) by presenting: (1) an extension of earlier thermodynamic analysis to include withdrawal; (2) a method for 

distinguishing once-through from recirculating surface-water

cooling systems; (3) a reclassification of 1,290 power plants 

by electrical generation type, cooling-system type, water 

type, and water source, including use of water from alternative sources; (4) application and in some cases modification 

of published heat- and water-budget models and estimates of 

thermoelectric water consumption at all 1,290 power plants 

distributed across the United States; and (5) application of 

thermodynamically constrained models of water withdrawals 

at the same plants. 

 The models described in this report estimate water 

consumption and withdrawal at the plant scale. Plant-scale 

estimates are summed to produce national totals that are 

compared to other available estimates. Coefficients of consumption and withdrawal were developed for various classes 

of power plants and compared to other published coefficients. 

It is important to note that the primary purpose of this report 

is not to provide national estimates of water consumption 

and withdrawal but rather to improve estimation at the scale 

of the individual power plant with the ultimate goal of better characterizing the role of thermoelectric water use in the 

national water budget. Consequently the estimates provided 

here may not agree with other published information at the 

national scale. The analyses presented in this report directly 

support several strategic science goals of the USGS, notably 

improving understanding of (1) interactions between the engineered and natural components of the hydrologic cycle, (2) the 

national water budget, and (3) effects of energy production 

on natural resources (Evenson and others, 2013; Ferrero and 

others, 2013).

Acknowledgments

Many individuals within and outside of the USGS 

contributed to this report. Particular acknowledgement is due 

Susan S. Hutson, USGS (retired), for decades of devoted 

public service and collegial support and especially for her 

leadership in the analysis of thermoelectric water use by the 

USGS. Thanks are also due to technical and editorial reviewers and numerous colleagues who provided critical feedback 

on different sections of the report throughout its preparation. 

Members of the USGS National Water Use Leadership Team 

provided input and guidance on pond classification. This study 

was funded by the National Water Census and the National 

Streamflow Information Program of the USGS.

Methods

Thermoelectric plants that withdraw water were categorized based on their methods of generating electricity 

and disposing of waste heat. Their withdrawal of water and 

consumption of freshwater were estimated using heat- and 

water-budget models and data on fuel use and net generation

reported to EIA.

Identification of Plants for Model Development 

and Water-Use Estimation

Diehl and others (2013) produced a list of 1,284 plants 

using plant-characteristic data from the 2010 EIA-860 Annual 

Electric Generator Report database (U.S. Department of 

Energy, Energy Information Administration, 2011a) to develop 

a heat-budget model for estimating consumption. That list 

included electric utilities and independent power producers 

operating generators and cooling systems using water. It did 

not include industrial or commercial facilities. Some plants 

previously included on that list were found on review to be 

unsuitable for water-use estimation, and others were added 

where additional data warranted. Initially only plants coded 

as operational were included on the list; however, 29 plants 

that were originally reported as non-operational were found 

to have produced electricity in 2010 and were added. Another 

13 plants on the original list were discovered to have dry 

cooling systems and were removed. Nine geothermal plants 

powered by binary cycle turbines were excluded because 

heat- and water-budgets could not be constructed. Lastly, one 

concentrating solar thermal plant (Maricopa Solar in Arizona) 

does not use water for energy conversion and was removed. 

After these various corrections were made, a total of 1,290 

thermoelectric, water-using power plants were carried forward 

for computation of water withdrawals and consumption (fig. 1; 

appendix 1). 
Figure 1. Geographic distribution of the 1,290 thermoelectric plants modeled to estimate water withdrawal and consumption in the United S

[Power plants in Puerto Rico and the U.S. Virgin Islands are not surveyed by the Department of Energy, Energy Information Administration.]

00

0 100 Miles0

0 400 Miles0 400 Kilometers 100 Kilometers 100 2

100 

22°

70°

40°

120° 110° 100° 90° 80° 

30°

60°

160°

160° 140° 120°

158° 156° 154°

20°

Base from U.S. Geological Survey, 1:2,000,000 Digital Line Data,Albers Equal-Area Conic Projection, NAD 83

ALASKA

CALIFORNIA

NEVADA

OREGON

WASHINGTON

IDAHO

MONTANA

WYOMING

NORTH 

DAKOTA

SOUTH

DAKOTA

SOUTH

CAROLINA

NORTH

CAROLIN

ARIZONA

UTAH COLORADO

NEBRASKA

KANSAS

OKLAHOMA

LOUISIANA

MISSOURI

ARKANSAS

ALABAMA

GEORGIA

FLORIDA

IOWA

MICHIGAN

MINNESOTA

WISCONSIN

ILLINOIS OHIO

PENNSYLVA

NEW 

TENNESSEE

KENTUCKY

VIRGINI

DC 

WEST

VIRGINIA

MISSISSIPPI

INDIANA

NEW MEXICO

HAWAII

Figure 1. Geographic distribution of the 1,290 thermoelectric power plants modeled to estimate water withdrawal and consumption in the U[Thermoelectric plants in Puerto Rico and the U.S. Virgin Islands are not surveyed by the U.S. Department of Energy, Energy Information Adm
4 Withdrawal and Consumption of Water by Thermoelectric Power Plants in the United States, 2010

Compilation of Descriptive and Operational Data

Plant-specific operational, locational, environmental, and 

other characteristic data were compiled from various sources 

and used to classify plants for the estimation of consumption 

and withdrawal. These data were available in varying degrees 

of quality and completeness, and some had to be estimated. 

Plant Characteristics

EIA-reported plant characteristic data were used to classify plants according to generation type and cooling type. 

EIA-reported prime movers and energy sources for each plant 

were used to classify plants into one of five generation types. 

Data directly related to electrical generation were assumed 

to be accurate because information regarding fuel use and 

production are fundamental to the financial operation of power 

plants and therefore are routinely tracked for general business 

accounting. 

Information regarding cooling-system types was not as 

consistent or complete. Power plants with water-using generation capacities less than 100 megawatts (MW) are not required 

to report cooling system information to EIA, and those that are 

required to do so sometimes provide inaccurate information. 

In recognition of this, cooling-system types were verified for 

all plants. Plant location data were obtained from EIA, U.S. 

Environmental Protection Agency (EPA), and National Energy 

Technology Laboratory (NETL) databases (U.S. Department 

of Energy, Energy Information Administration, 2001, 2009, 

2011a; U.S. Department of Energy, National Energy Technology Laboratory, 2007b; U.S. Environmental Protection 

Agency, 2007a, n.d.), and verified and in some cases corrected 

(Diehl and others, 2013). Using the verified locations, recirculating cooling towers, once-through cooling system intake 

structures and discharge outlets were identified from aerial 

imagery as described by Diehl and others (2013). For many 

plants, the aerial-photo interpretation also allowed characterization of the surface-water source. 

Heat- and Water-Budget Data

Plant-characteristic and operational data needed for 

linked heat and water budgets included net generation, fuel 

consumption, boiler efficiencies, and environmental data, 

notably air and water temperature (Diehl and others, 2013). 

These data varied widely in availability and quality among the 

different generation types. Among all generation-types, net 

generation data were of good quality. However, the quality of 

information on boiler efficiencies and the energy content of 

fuels varied and had to be estimated for some generation types 

(Diehl and others, 2013). 

Most environmental data used in this analysis are 

published by the National Oceanic and Atmospheric Administration (NOAA). Only data from weather stations reporting 

12 months of meteorological observations were used as model 

input variables. USGS and EIA water-temperature data were 

screened to eliminate extreme values and irregular seasonal 

patterns (Diehl and others, 2013).

Classification of Plants

Thermoelectric power plants were classified by coolingsystem type and generation type in order to select which 

heat- and water-budget model to apply to each plant and for 

comparison of model-estimated water use to EIA-reported data. 

The distinction between once-through and recirculating cooling ponds was defined based on the relation of runoff and pond 

depth. An additional classification of plants was developed 

based on water source and water type to support an analysis of 

the emergent use of alternative water sources.

Generation and Cooling-System Type

The share of fuel energy converted to waste heat in the 

condenser depends largely on generation technology and is 

reflected in the estimation method applied. Reported prime 

movers and energy sources were used to classify plants into 

one of five generation types (table 1). Common to all waterusing generation types are steam-driven turbines, which may 

be powered by a variety of heat sources such as fossil-fuel 

combustion, or nuclear, geothermal, or solar energy. Combined-cycle plants have both combustion and steam turbines, 

which at a few plants operate together to drive a single generator but typically operate separately. 

Cooling-system type determined which modeling 

approaches were used (table 2). Cooling systems were broadly 

classified as wet recirculating cooling towers and surfacewater cooling systems. Surface-water cooling systems were 

Table 1. Classification for condenser duty estimation method by 

generation type for thermoelectric plants in the United States.

Generation type Prime mover Energy source Estimation 

method

Combustion 

steam

Steam

Various, 

dominated 

by coal

Linked heat 

and water 

budgets with 

appropriate 

cooling type

Combined cycle

Combined cycle 

combustion part

Various, 

dominated by 

natural gas

Combined cycle 

steam part

Combined cycle 

single shaft

Nuclear Steam Nuclear

Geothermal Steam Geothermal 

Solar steam Steam Solar

Waterconsumption 

coefficient
Methods 5

further subdivided into once-through cooling systems and 

recirculating cooling ponds. 

The 1,290 plants selected for this analysis represent 

84 percent of total net generation reported to EIA in 2010 

(U.S. Department of Energy, Energy Information Administration, 2011b; table 3). Of these, 892 are relatively straightforward in design and can be characterized as simple combinations of one generation type, one dominant fuel source 

(providing 90 percent or more of total fuel heat), and one 

cooling-system type. These “simple plants” 2 account for 

about 77 percent of the 2010 net generation reported by the 

1,290 plants in this analysis. 

The computation of coefficients for consumption and 

withdrawal is fairly direct for simple plants. However, geothermal and solar thermal plants (Diehl and others, 2013) and plants 

that have multiple cooling-system types, generation technologies, and/or use multiple fuels present a number of challenges 

in allocating water use to distinct generation types and were 

not included in the evaluation of categorical coefficients. These 

“complex plants” represent about 23 percent of net generation 

for all plants considered in this analysis (table 3). 

EIA-reported water-use data and net generation were 

analyzed for 2005 and 2010 to evaluate changes in withdrawal and consumption flow rates, electrical generation, and 

water-use coefficients by generation type and cooling type. To 

allow comparison of overall use in EIA data reported for 2005 

and 2010, withdrawal and consumption was estimated for 

2

 In this report, the phrase “simple plants” is used to refer to those with one 

dominant fuel type, a single type of generation technology, and a single cooling type. Other plants are termed “complex plants.”

63 nuclear plants for 2005, a year when they were not required 

to report water use, and added to EIA water-use data for 

that year. These values were computed as the product of net 

generation and the USGS-computed coefficients of withdrawal 

and consumption, respectively. Three nuclear plants co-located 

with fossil-fuel powered generators did report water use, and 

those data were used in the analysis. 

For comparison of reported data to model estimates, 

plants that reported water use to EIA were categorized by 

generation type and cooling-system type. Only water-using 

plants that have generating capacities of 100 MW and greater 

are required to report water use to EIA (U.S. Department 

of Energy, Energy Information Administration, 2006a and 

2011a). For 2010, 835 such plants represented 82 percent of 

total net generation (U.S. Department of Energy, Energy Information Administration, 2011b; table 3). Of these, 151 were 

identified as complex plants (table 3) and excluded from the 

evaluation of categorical coefficients. In 2005, only 685 waterusing plants reported to EIA, of which 147 were identified as 

complex plants (U.S. Department of Energy, Energy Information Administration, 2006a; table 3) and similarly excluded.

Classification of Cooling Ponds

In water-use reporting, the term “withdrawal” commonly 

refers to water diverted from a natural hydrologic source. 

Though this idea is relatively straightforward, withdrawal as 

defined here is not typically measured directly at power plants 

and often must be inferred from other available information, 

such as pumpage or flow through a condenser. At most plants 

volumes reported as withdrawal are flow through condensers in once-through cooling systems or makeup flows to 

recirculating cooling systems. Many plants reported apparently contradictory combinations of cooling-system type and 

withdrawal—flow through the condenser reported as withdrawal from recirculating ponds or makeup flow reported as 

withdrawal to once-through systems. Such contradictions in 

the reported data indicate a need for an independent approach 

to distinguish once-through from recirculating cooling ponds. 

This distinction can change water withdrawal at a plant by as 

much as two orders of magnitude.

Differentiating recirculating and once-through cooling 

ponds required dividing a continuum from isolated ponds 

without watersheds to ponds connected to the natural system 

through inflow and outflow. Typically, recirculating ponds are 

artificial and surrounded by levees, lack large watersheds, and 

receive little natural inflow aside from direct precipitation and 

diversions from natural hydrologic systems. Once-through 

ponds are typically larger reservoirs with sizable watersheds 

that supply sufficient runoff to maintain water levels and 

outflows during years of normal precipitation. Most cooling 

ponds can easily be classified as recirculating or once-through;

however, many ponds have intermediate characteristics that 

make them harder to classify. Some ponds have small watersheds that provide substantial natural inflows, but not enough 

to obviate the need for makeup flows. Others have watersheds 

Table 2. Classification for modeling approach to consumption 

and withdrawal by cooling-system type for thermoelectric plants 

in the United States.

Cooling-system 

type

Consumption 

modeling 

approach

Withdrawal 

modeling 

approach

Wet freshwater 

recirculating 

cooling tower

Wet tower 

evaporation 

model

Ratio to 

consumption

Recirculating 

pond or canal

Water surface 

evaporation model and 

Penman-Monteith model

Equal to 

consumption

Once-through 

freshwater

Water surface 

evaporation model

Based on 

condenser duty 

and range

Once-through 

saline water Not modeled

Based on 

condenser duty 

and range

Wet saline 

recirculating 

cooling tower

Not modeled Not modeled

Dry cooling 

systems

Not modeled Not modeled
Table 3. Net electrical generation for water-using thermoelectric plants according to generation type and cooling-system type as reported to the U.S. Energy Information Administration for 685 plants for 2005, 835 plants for 2010, and 1,290 plants for 2010 as analyzed by the U.S. Geological Survey (USGS[Values may not sum to totals because of independent rounding. All net electrical generation is in gigawatt hours; NGCC, natural gas combined cycle; NA, not applicable; NR, noand solar thermal plants and plants that have multiple cooling-system types, generation technologies, and/or use multiple fuels] Genera- tion type Cooling-system type 

Once-through saline Once-through fresh Recirculating pond Recirculating tower Complex EIA USGS EIA USGS EIA USGS EIA USGS EIA USGS 

2005 2010 2010 2005 2010 2010 2005 2010 2010 2005 2010 2010 2005 2010 2010 

Oil 23,721 4,892 5,091 5,126 72 137 NR NR NA 369 205 413 NA NA NA Nuclear 162,092 160,038 160,038 199,521 215,991 144,978 83,282 86,114 77,502 260,680 272,506 272,506 NA NA NA 7NGCC NR 33,483 30,773 512 16,938 14,184 9,547 4,767 16,707 145,261 432,426 492,128 NA NA NA Gas steam 15,589 10,233 11,723 16,907 20,449 22,701 9,340 7,845 3,484 16,105 12,657 14,471 NA NA NA Coal 31,567 33,519 26,854 652,545 556,564 558,754 127,676 122,777 104,311 677,908 727,587 731,552 NA NA NA 1,4Complex NA NA NA NA NA NA NA NA NA NA NA NA 691,082 610,374 781,815 6Totals 232,969 242,164 234,478 874,610 810,014 740,753 229,845 221,503 202,003 1,100,322 1,445,380 1,511,069 691,082 610,374 781,815 3,
Methods 7

large enough to maintain water levels in most years, but require 

makeup flows during droughts. Of the 92 thermoelectric plants 

located on cooling ponds in 2010, 36 were classified on examination as having recirculating ponds, and 24 as having oncethrough ponds. 

Categorization of the remaining 32 plants required 

additional analysis. Simple water budgets were developed to 

evaluate natural and plant-induced influences on the 28 ponds 

providing cooling water to these 32 plants (3 ponds are shared 

by multiple plants). These water budgets included monthly 

inflows from direct precipitation and watershed runoff and 

outflows of natural evaporation and forced evaporation. 

Groundwater exchange, pumped inputs, blowdown from the 

pond, and water use for non-cooling purposes could not be estimated due to a lack of reported information; these flows were 

assumed to be small relative to the errors in the water budget 

and ignored for the purpose of defining the cooling type. 

Long-term average precipitation data were obtained from 

the National Climatic Data Center’s (NCDC) 1981–2010 Climate Normals (National Oceanic and Atmospheric Administration, National Climatic Data Center, 2012b). Average direct precipitation to each of the 28 ponds categorized by water budgets

was determined by interpolation among nearby weather stations. 

Using a 100-mile search radius, the distances from each pond to 

the nearest three weather stations were determined and used to 

compute a distance-weighted mean of direct precipitation based 

on the inverse distance from the respective pond. 

Watershed runoff for each pond was calculated by multiplying long-term average precipitation by a runoff curve number (Cronshey, 1986) for each watershed. Runoff curve numbers were estimated based on dominant land use determined 

from the National Land Cover Database (Fry and others, 2011) 

and dominant soil hydrologic group determined from the Soils 

Survey Geographic (SSURGO) database (Soil Survey Staff, 

Natural Resources Conservation Service, U.S. Department of 

Agriculture, 2013). The depth of runoff from the watershed 

was multiplied by the ratio of the pond area to the watershed 

area to estimate the depth added to the pond by runoff.

Long-term average natural evaporation for each pond 

was obtained by interpolation from maps of U.S. evaporation 

(Farnsworth and others, 1982). Forced evaporation was estimated using methods described by Diehl and others (2013).

Thirty-two plants on the 28 cooling ponds were initially 

classified as recirculating or once-through based on aerial 

photographs. Using the calculated inflows and outflows, the 

average depth added to the pond by runoff was plotted against 

long-term net precipitation (direct precipitation to the pond 

minus natural pond evaporation) (fig. 2). Plants in arid regions 

20

0

40

60

80

100

120

140

–40 –30 –20 –10 0 10 20 30 40

Average runoff to lake, in inches over lake area

Long-term annual direct precipitation minus annual map evaporation, in inches

Initially once-through

Initially recirculating

19-inch threshold

EXPLANATION

Figure 2.

Once-through

Recirculating

Figure 2. Classifications of 32 plants at 28 once-through or recirculating cooling ponds for which water budgets 

were developed, including the watershed runoff threshold determining pond cooling category, for thermoelectric 

power plants in the United States. [Initial classifications were determined by observation of aerial photographs.]
8 Withdrawal and Consumption of Water by Thermoelectric Power Plants in the United States, 2010

plot to the left of plants in more humid regions; both recirculating and once-through plants are scattered along this climatic 

axis, suggesting that cooling-pond types are independent of 

climate. A value of 19 inches of depth added to the pond by 

runoff from the watershed was selected as the best threshold 

separating recirculating from once-through cooling systems. 

Four cooling systems initially classified as recirculating 

plotted above the 19-inch threshold and were reclassified as 

once-through, and two once-though systems were reclassified 

as recirculating. 

Water Sources and Water Types

Plants reporting water use to the EIA include information 

about water sources (table 4) and types (table 5) and the names 

of the water sources from which they withdraw cooling water 

(U.S. Department of Energy, Energy Information Administration, 2011a). The names of water sources ranged from the 

specific water body name, to general descriptions such as 

“wells,” “river,” and “municipality.” Alternative water types 

include reclaimed wastewater such as treated effluent from 

sewage-treatment plants and water not suitable for drinking or 

irrigation because of high concentrations of dissolved solids 

(brackish and saline water). 

Two methods were used to identify plants using alternative water. First, 172 such plants were identified directly from 

EIA-reported water source and type (U.S. Department of 

Energy, Energy Information Administration, 2011a). Second, 

water sources and types for 12 plants were added based on

plant locations and named water sources producing an alternate 

list of 184 plants. To conform to USGS definitions, 48 plants 

that reported brackish water to EIA were reclassified as saline 

plants. Also, seven plants that reported more than one water 

type code to EIA (for example, BR and BE) were moved to 

single water-type categories for the model estimates. Two plants 

that reported “other” water source and water type codes were 

modeled as surface-water saline plants. For the first list of 172 

plants, EIA-reported withdrawal and consumption were used 

to calculate national totals of alternative water use by type. For 

the second list of 184 plants, alternative water withdrawal and 

consumption were estimated based on methods described in the 

following sections of this report and in Diehl and others (2013). 

Models for Estimating Thermoelectric Water Use

Consumption was estimated using models developed 

by Diehl and others (2013) except for plants with recirculating cooling ponds, for which a new method was developed. 

Separate methods for estimating withdrawal were developed 

for once-through cooling systems, recirculating cooling ponds, 

and recirculating cooling towers. Coefficients of withdrawal 

and consumption weighted by net generation were calculated 

for categories of simple plants as outlined above.

Consumption

Water consumption at most plants was modeled by 

constructing heat and water budgets of the major energy flows 

into and out of thermoelectric power plants based on generation type and cooling-system type (Diehl and others, 2013). 

Two exceptions were solar thermal plants and plants with 

recirculating cooling ponds. For solar plants, consumption 

coefficients were used because reported plant data were insufficient to construct heat budgets (Diehl and others, 2013). 

Heat and water budgets constructed for recirculating cooling 

ponds included natural evaporation from the pond surface in 

addition to forced evaporation.

For plants with recirculating cooling ponds, natural evaporation was estimated monthly for 2010 by using the Food 

and Agriculture Organization’s (FAO) version of the PenmanMonteith method (Allen and others, 1998). Input data for the 

Penman-Monteith model included meteorological and climatic 

data obtained from NCDC’s Quality Controlled Local Climatological Data (QCLCD) database (National Oceanic and 

Atmospheric Administration, National Climatic Data Center, 

n.d.), and solar radiation data, obtained from NCDC’s National 

Solar Radiation Database (National Oceanic and Atmospheric 

Administration, National Climatic Data Center, 2012a). The 

model was modified to use a reference-crop albedo of 0.05 to 

represent a water-body surface rather than land covered in 

vegetation (Allen and others, 1998). Monthly evaporation 

outputs from the Penman-Monteith model were adjusted by 

using interpolated averages of long-term evaporation acquired 

from U.S. evaporation atlases (Farnsworth and others, 1982). 

The mapped values are based on measured pan evaporation 

and provide an empirical constraint on the long-term model 

estimates. Adjusted monthly evaporation values were summed 

to obtain annual natural evaporation for each cooling pond. 

Table 4. Cooling water source codes and descriptions.

[U.S. Department of Energy, Energy Information Administration, 2011a]

Code Type of water source

SW Surface water (example: river, canal, bay)

GW Groundwater (example: well, aquifer)

PD Plant discharge water (example: wastewater treatment 

discharge)

OT Other

Table 5. Cooling water type codes and descriptions.

[U.S. Department of Energy, Energy Information Administration, 2011a]

Code Type of water

BR Brackish water

FR Freshwater

BE Reclaimed wastewater

SA Saline water

OT Other
Methods 9

Withdrawal

Models of thermoelectric water withdrawal were developed for each plant’s generation and cooling-system type 

based on plant-specific design parameters and operational 

data (tables 1 and 2). Withdrawal models apply principles of 

conservation of energy and mass first to estimate waste heat 

(condenser duty) and then to estimate withdrawal needed for 

cooling through evaporation, convection, and radiation, given 

system properties. Principal cooling-system types include 

once-through cooling systems, evaporative cooling towers, 

and recirculating cooling ponds. Water consumed in flue-gas 

desulfurization (FGD) and other in-plant processes, such as 

ash handling, inlet cooling, and boiler makeup, is relatively 

small compared to cooling requirements and may be drawn 

from cooling-system discharge flows, and so was not included 

in the estimate. 

Once-Through Cooling System Withdrawals

Withdrawal from once-through cooling systems was 

modeled based on the thermal properties of water. Simply 

put, for a given quantity of heat energy imparted to water, the 

increase in temperature of that water is inversely proportional 

to its mass. For once-through thermoelectric cooling systems, 

this relation provides a means to quantify withdrawal (mass of 

water flowing through the condenser) as a function of condenser duty (heat transferred to the cooling water in the condenser) and condenser range (temperature difference between 

condenser inflow and outflow): 

W CD

CR

c m p = w





 



 ÷ , (1)

where 

Wm is mass of water withdrawn,

CR is condenser range in degrees of temperature,

CD is condenser duty in heat, and

cpw is the specific heat capacity of water at 

1 atmosphere pressure.

Volumetric water withdrawal was modeled by first solving for mass withdrawal using equation 1 and then converting 

water mass to volume based on the temperature of the withdrawn water when it entered the condenser:

W W v m = ÷ ρ wT , (2)

where

Wv is volumetric water withdrawal,

Wm is mass water withdrawal (eq. 1), and

ρwT is the density of water at the temperature at 

which it enters the condenser.

If both condenser duty and condenser range are known, 

withdrawal by once-through cooling systems can be tightly 

constrained. Thus, much of the effort in computing oncethrough withdrawal estimates involved refinement of these two 

terms. Condenser duty was computed for each plant following 

the methods described by Diehl and others (2013). Condenser 

range was estimated based on the difference between reported 

withdrawal and discharge water temperatures at selected 

plants with once-through cooling; this difference was treated 

as “reported condenser range” at the selected plants. Because 

condenser range is closely related to the size of the condenser, 

it is essentially a fixed property for each plant operating at full 

power. At less than full power, operational flexibility increases 

somewhat, with the option of reducing condenser range by 

maintaining the design flow with a reduced waste-heat load. 

Decreasing the range in this way reduces steam pressure 

downstream from the turbine, potentially providing a small 

improvement in plant efficiency. 

If the withdrawal and discharge water temperatures 

reported by the plant operator are close to the actual temperatures of cooling water entering and leaving the condenser, 

withdrawal can be accurately estimated based on modeled 

condenser duty. However, the wide variation in reported 

condenser ranges calls such accuracy into question. Thermoelectric power plants typically use medium-range condensers with design ranges of 10 to 25 degrees Fahrenheit (°F) 

(Cheremisinoff and Cheremisinoff, 1981, p. 107; Stultz and 

Kitto, 1992, p. 57-11) which correspond to withdrawals from 

12,000 to 4,800 gallons per million British thermal units 

(gal/MMBtu), respectively. For a typical combustion-steam 

plant having a 33-percent thermal efficiency, 88-percent 

boiler efficiency, and 2-percent auxiliary losses (Diehl and 

others, 2013), this would produce coefficients ranging from 

66,000 to 26,000 gallons per megawatt hour (gal/MWh).

The overall distribution of reported condenser range 

relative to intake temperature is highly variable, including 

values apparently outside the typical design condenser range 

of 10–25 °F. About 4 percent of reported condenser ranges are 

below the product of 10 °F and monthly plant capacity factor, 

thus implying that the condenser’s design range is less than 

10 °F. One plant reported a difference between intake water 

temperature and discharge water temperature of only 1 °F, at 

a capacity factor of 50 percent, suggesting a design condenser 

range of only 2 °F. These low reported ranges may also reflect 

issues with estimated capacity factors involving inaccurate 

reported capacity or net generation.

Fifteen percent of reported ranges are greater than 25 °F, 

and 1 percent are greater than 40 °F. High-range condensers 

are feasible with a cold enough once-through water source, 

and their use in that context would be an economic choice at 

the time of plant design, saving on initial cost at the expense 

of slightly lower thermal efficiency. Very high reported condenser ranges (above 40 °F) may reflect reporting practices 

inconsistent with the assumption that the difference between 

intake- and discharge-water temperatures equals actual 

condenser range.

Predictions of condenser range were based on a relation 

developed for a subset of once-through cooling systems (U.S. 

Department of Energy, Energy Information Administration, 

2011b) where reported temperatures and withdrawals reflect 
10 Withdrawal and Consumption of Water by Thermoelectric Power Plants in the United States, 2010

relatively reliable data-collection methods. Reported withdrawal rates were used where they were

1. Measured using an instantaneous flowmeter and pump 

running time, 

2. Measured using a streamflow gage or weir, 

3. Measured using a cumulative or continuous flowmeter, or

4. Estimated based on stated pump capacity and pump 

running time.

Reported intake and discharge temperatures were used 

where measured continuously or at regular intervals with a 

thermometer. Systems that used chlorine were not included 

because chlorine use is typical of recirculating systems, in 

which discharge temperature minus intake temperature is not 

generally equal to condenser range. Selected data meeting 

these criteria included 1,533 paired observations of monthly 

withdrawal and condenser range for 206 cooling systems at 

128 plants (fig. 3). The number of data pairs per month ranged 

from 104 to 159. Reported intake temperatures ranged from 

28 to 97 °F, with 15 values of 32 °F and 3 values less than 

32 °F. The minimum reported condenser range was 1 °F, and 

the maximum was 47 °F; these ranges correspond to withdrawals of about 120,000 and 2,600 gal/MMBtu, respectively, 

and for a typical combustion-steam plant about 660,000 and 

14,000 gal/MWh, respectively. Low ranges are more common 

in cooling systems that did not receive condenser duty greater 

than 1,000 MMBtu per month.

To solve for monthly withdrawal using equation 1, linear 

functions were derived to produce a “best estimate” of condenser 

range for each plant as a function of monthly average intake 

temperature and to establish thermodynamically plausible upper 

and lower bounds for condenser ranges. A number of approaches 

could have been used for this task, including simple linear 

regression with confidence limits (Helsel and Hirsch, 2002) 

and quantile regression (Cade and Noon, 2003). The approach 

used here was selected to preserve the observed distributions of 

condenser-range values across the range of intake temperature. 

To do this, the 1st, 50th, and 99th percentiles of condenser 

range were determined for data grouped in 5-degree intervals of 

monthly intake temperature, and linear functions were regressed 

through these percentiles (fig. 4). The resulting equations are

upper threshold: CRU = –0.2514 Ti + 49.678 °F, (3)

best estimate: CR = –0.1044 Ti + 22.464 °F, and (4)

lower threshold: CRL = –0.0093 Ti + 2.9419 °F. (5)

0

5

10

15

20

25

30

35

40

45

50

20 30 40 50 60 70 80 90 100

Selected reported condenser ranges, in degrees Fahrenheit

Intake water temperature, in degrees Fahrenheit

Condenser Range

All systems with selected data

Selected reported

condenser range

Selected reported

condenser range

at plants with

duty of 1,000 MMBtu

in at least 1 month

EXPLANATION

Figure 3.

Figure 3. Selected reported condenser ranges and corresponding intake water 

temperatures for 128 thermoelectric power plants in the United States. [Data from 

the U.S. Department of Energy, Energy Information Administration]
Methods 11

Over the entire range of intake water temperature, about 

2.8 percent of reported condenser ranges were below the lower 

linear threshold, and 2.2 percent were above the upper linear 

threshold. These outlying values may result from errors in 

measurement or reporting, but might also reflect a mismatch 

between the actual cooling system and the simple model of 

once-through cooling systems used in this study.

Diehl and others (2013) noted that estimation error for 

condenser duty may be as high as 15 percent or greater. To 

account for such error and other factors in estimating withdrawal, a margin of 18 percent was added to the maximum 

withdrawal estimates and subtracted from minimum estimates. These adjustments to the upper and lower thresholds 

expanded the predicted limits to include 98.5 percent of 

selected reported withdrawals. This approach conservatively 

assumes that errors in condenser range and duty are correlated 

in such a way as to be multiplicative in estimated withdrawal; 

they are more likely independent or nearly so. These limiting 

thresholds for thermodynamically plausible withdrawal are far 

enough apart to include nearly all once-through cooling systems that fit the analytical framework of this study. The upper 

condenser range threshold is about twice the best estimate, 

and the lower threshold is about one-sixth of the best estimate. 

Estimates outside these thresholds probably represent differences in defining withdrawal or errors in reporting.

Systematic differences between estimates and EIAreported withdrawals cannot be attributed to the assumption 

that withdrawal is inversely proportional to estimated condenser 

range. Although estimated and reported withdrawals vary 

widely at individual plants, a comparison of aggregate totals for 

the selected plants used to develop the condenser-range estimator shows the model to be unbiased. The degree of bias in estimates was evaluated based on the reported withdrawals associated with the selected ranges used to develop the median-range 

estimator. An apparent monthly condenser duty was derived 

for each cooling system as the product of reported withdrawal 

and condenser range. Dividing this reported condenser duty by 

an estimated condenser range from the median linear function 

yielded a corresponding estimated withdrawal. Comparing the 

total of all monthly reported withdrawals (1,459 billion cubic 

feet) to estimated (1,461 billion cubic feet) withdrawals for the 

same systems shows a startling degree of similarity. 

0

5

10

15

20

25

30

35

40

45

50

20 30 40 50 60 70 80 90 100

Condenser range, in degrees Fahrenheit

Intake temperature, in degrees Fahrenheit

Reported condenser ranges

99th percentile in each

5-degree-Fahrenheit interval

Median condenser range

1st percentile in each

5-degree-Fahrenheit interval

Estimated upper threshold

of condenser range

Best estimate of 

condenser range

Estimated lower threshold

of condenser range

EXPLANATION

Condenser Range

Linear thresholds contain 95% of data

Figure 4.

Figure 4. Median, minimum, and maximum estimated condenser ranges and 

reported condenser ranges for thermoelectric power plants in the United States.
12 Withdrawal and Consumption of Water by Thermoelectric Power Plants in the United States, 2010

Recirculating Pond Withdrawals

The identification of a cooling pond as recirculating 

or once-through has a substantial effect on its withdrawal 

estimate. If identified as once-through, flow through the 

condenser(s) is defined by the USGS as withdrawal, and consumption is determined as forced evaporation from the pond. 

For ponds identified as recirculating systems, withdrawal is 

defined herein as the sum of makeup flows to replace water 

lost by natural pond evaporation and forced evaporation, 

which is equal to estimated consumption. 

In practice, makeup flow may also be used to offset other 

unknown fluxes including pond leakage and blowdown (water 

discharged or “blown down” from the cooling system to limit 

the concentration of dissolved solids). Uncertainties in natural 

evaporation are large but were not quantified, nor were magnitudes of leakage and blowdown. The water level in a cooling 

pond can vary over time, and losses may not be made up as 

they occur. In States with appropriated water rights, water 

availability may limit makeup flows. Although makeup flows 

were calculated by month, even annual totals are subject to 

uncertainty due to differences in water level at the beginning 

and end of the year.

Tower Withdrawals 

Withdrawal at plants with recirculating cooling towers is 

almost entirely cooling system makeup replacing evaporated 

water and blowdown. Other losses include a small amount 

of water lost as “drift” (droplets entrained in the air). Drift 

was assumed to be insignificant in the heat-budget model; in 

modern towers, drift is much smaller than the uncertainty in 

the modeled evaporation. 

The amount of blowdown water used in tower cooling 

systems was calculated from the evaporative consumption 

from the tower and the cycles of concentration for the system. “Cycles of concentration” refers to the ratio of dissolvedsolids concentrations in blowdown discharge to concentrations in makeup water (withdrawal). The number of cycles of 

concentration is also about equal to the ratio of the makeup 

to blowdown. The more cycles of concentration, the less 

blowdown: at 2 cycles of concentration, a plant’s blowdown 

is equal to its consumption, while at 10 cycles, blowdown is 

one-ninth of consumption. Although efficient operations at 

most sites would make it possible to operate at 5 to 8 cycles of 

concentration (California Utilities Statewide Codes and Standards Team, 2011), this may impose higher costs, and many 

plants still operate in the range of 2 to 4 cycles and as low as 

1.5 cycles for cooling towers that use seawater. Thus, while 

withdrawal is typically 115 to 150 percent of consumption for 

freshwater towers, it can be as high as 200 percent. At some 

plants, blowdown water is disposed of in evaporation ponds 

instead of being treated and discharged, and the remaining 

solids are disposed of in landfills; this method of blowdown 

disposal was not modeled.

Three estimates of withdrawal for cooling towers were 

developed: a best estimate and lower and upper limits outside 

of which reported withdrawals are difficult to reconcile with 

heat and water budgets. The best estimate of tower withdrawal 

was 140 percent of median estimated tower consumption, 

based on the typical value of 3.5 cycles of concentration (California Utilities Statewide Codes and Standards Team, 2011). 

Known sources of error include estimation error for condenser 

duty and evaporation ratio, which are treated in the consumption model (Diehl and others, 2013), and error in the assumed 

cycles of concentration. To address the latter error, a Monte 

Carlo experiment (Efron and Efron, 1982) was run through 

about 1 million realizations, using a range of cycles of concentration from 2 to 10. Ninety-five percent of realizations yielded 

withdrawals that fell between estimated minimum consumption multiplied by 1.29 and estimated maximum consumption 

multiplied by 1.77. These values were taken as conservative 

limits for plausible tower withdrawal, assuming that error in 

the estimation of cycles of concentration is independent of 

other errors. 

Complex Plant Withdrawals

Withdrawals at plants with more than one type of cooling 

system were estimated as a sum of withdrawal by each type. 

These component withdrawals were estimated separately using 

methods described above and were generally assumed to result 

from independent operations without interconnections. This 

assumption does not strictly apply in all cases. For example, 

discharge from once-through cooling systems may be used for 

makeup to recirculating systems, and this dual use may not be 

reflected in reported data. For a given amount of condenser 

duty, once-through withdrawal is much larger than recirculating withdrawal. Estimated withdrawals for complex plants that 

included once-through cooling systems were dominated by the 

once through component. Given that the uncertainty in estimating once-through withdrawal is greater than the magnitude 

of withdrawal for recirculating cooling at the same plant, the 

exact treatment of the recirculating withdrawal is unlikely to 

have a substantial effect on estimated plant withdrawal.

Development of Consumption and Withdrawal 

Coefficients

Consumption and withdrawal coefficients in gallons 

per kilowatt hour were estimated for the 892 simple plants. 

Consumption coefficients were estimated as the ratio of total 

annual consumption to annual net generation for all combinations of generation and cooling-system types. 

Withdrawal coefficients were estimated in different ways 

for three types of cooling system. For once-through cooling 

systems, the withdrawal coefficient was calculated as the best 

estimate withdrawal divided by net generation. For recirculating ponds, the withdrawal coefficient equals the consumption 

coefficient. For recirculating cooling tower systems, withdrawal coefficients were computed as 1.4 times the corresponding consumption coefficient for each generation type, 

assuming 3.5 cycles of concentration.
Results and Discussion 13

For all combinations of generation and cooling type, 

average annual consumption and withdrawal were divided 

by annual net generation to yield average consumption and 

withdrawal coefficients. These coefficients can be compared 

directly to published values, recognizing that not all published 

consumption coefficients take into account forced evaporation from the discharge plume below once-through cooling 

systems. Uncertainty in model predictions associated with 

high and low estimated threshold values for consumption at 

each plant is not reflected in these coefficients. Any systematic 

bias in the model would translate into systematic bias in the 

consumption coefficients presented here.

Results and Discussion

Model-based plant-specific estimates of thermoelectric 

water withdrawal and consumption for 2010 were the primary 

results of this study; they complement EIA-reported water use 

data for 2005 and 2010. These estimates and the coefficients 

of withdrawal and consumption developed from them were 

aggregated by plant category and compared between methods 

and between years. Alternative water use was evaluated for 

2010. While the amount of withdrawal and consumption can 

be roughly defined and some trends are discernable, the differences between coefficients obtained using different methods 

suggest that thermoelectric water use is still subject to considerable uncertainty.

Estimated Thermoelectric Water Use for 2010

The national-level water-withdrawal total for 1,290 

water-using thermoelectric plants in the United States estimated for 2010 was about 129 Bgal/d (table 6), of which 

about 3.5 Bgal/d, or about 3 percent, was consumed (table 7). 

Individual estimates of consumption and withdrawal for each 

plant are provided in appendix 1 (table available at http://pubs.

usgs.gov/sir/2014/5184/). The largest estimated withdrawals 

occurred at plants using once-through cooling, accounting for 

70 percent of annual withdrawals (table 6). Most once-through 

freshwater cooling systems are associated with coal-fired 

plants, whereas once-through saline water cooling systems are 

mostly at nuclear power plants. These findings are consistent 

with once-through cooling-system technologies and the large 

volumes of water needed for cooling purposes. 

Excluding complex plants, recirculating cooling towers 

accounted for 60 percent of estimated consumption (table 7). 

The relatively large volumes of water consumed at plants with 

recirculating towers are consistent with the evaporative processes associated with this cooling-system technology.

Consumption and Withdrawal Coefficients

Withdrawal and consumption coefficients were calculated for only the 892 simple plants described above (tables 8 

and 9). Though not derived from the full set of plants, these 

coefficients should be reasonably representative of water-use 

rates at all plants. Net generation at these plants amounted to 

77 percent of total net generation for the 1,290 plants modeled 

for consumption and withdrawal.

Some of the consumption and withdrawal coefficients 

for simple plants developed in this study differ markedly from 

published values (Macknick and others, 2011). In particular, consumption coefficients developed by the heat-budget 

method for once-through cooling are at or above the highest 

published values, but most of those for cooling towers are at or 

below the lowest published values. Modeled consumption per 

kilowatt-hour of generation from plants with cooling towers 

exceeded that from plants with once-through systems by about 

20 to 70 percent across the four cooling types.

EIA-Reported Water Use in 2005 and 2010

Total EIA-reported withdrawals decreased from 

198 Bgal/d in 2005 to 163 Bgal/d in 2010, an 18-percent 

decline (table 6). In both years, withdrawals at simple plants 

with once-through freshwater cooling dominated by coalfired and nuclear plants accounted for just over half of total 

withdrawals (fig. 5; table 6). The largest declines in withdrawal (18.2 Bgal/d and 9.5 Bgal/d for freshwater and saline 

systems, respectively) occurred at once-through systems 

(fig. 5; table 6). Similarly, withdrawals for complex plants, 

most of which have cooling systems consisting of oncethrough cooling and recirculating towers, declined 31 percent 

(table 6). Because once-through cooling systems withdraw 

larger volumes of water than cooling towers, the decline at 

complex plants suggests a shift from once-through cooling to tower- cooling systems. Taken together, the decline in 

withdrawals at once-through saline, once-through fresh, and 

complex plants accounts for 96 percent of the total decrease in 

withdrawals, while the number of plants in all three categories 

remained nearly constant from 2005 to 2010 (U.S. Department of Energy, Energy Information Administration, 2006b 

and 2011b). 

Natural gas combined-cycle (NGCC) plants, associated 

mostly with recirculating towers, represent the largest increase 

in net generation from 2005 to 2010 (fig. 6; table 3). Contrary 

to the overall trend, reported withdrawals for once-through 

cooling for NGCC plants increased fourfold between 2005 and 

2010 (table 6). This proportional increase was relatively small 

in total magnitude (about 0.9 Bgal/d) and may reflect use of 

recirculating towers in some new plants, conversion of older 

plants to NGCC generation without changes to existing cooling systems, or inconsistent reporting. 
Table 6. Thermoelectric plant water withdrawals by generation and cooling-system types as reported to the U.S. Department of Energy, Energy Infofor 2005 and 2010, and as modeled by the U.S. Geological Survey (USGS) for 2010. [Values may not sum to totals because of independent rounding. All withdrawal is in millions of gallons per day; NGCC, natural gas combined cycle; NA, not applicable; NR, noand solar thermal plants and plants that have multiple cooling-system types, generation technologies, and/or use multiple fuels] Genera- tion type Cooling-system type 

Once-through saline Once-through fresh Recirculating pond Recirculating tower Complex EIA USGS EIA USGS EIA USGS EIA USGS EIA USGS 

2005 2010 2010 2005 2010 2010 2005 2010 2010 2005 2010 2010 2005 2010 2010 200

Oil 5,037 1,349 659 998 35 21 NR NR NA 13 1 1 NA NA NA 6,0Nuclear 16,998 12,357 17,019 20,638 21,815 15,405 1,177 5,246 166 578 1,076 605 NA NA NA 39,NGCC NR 1,402 1,213 292 1,188 446 15 102 16 1,038 643 384 NA NA NA 1,Gas steam 14,652 10,533 1,209 9,661 5,952 2,442 1,073 1,631 21 102 50 32 NA NA NA 25,4Coal 3,843 5,413 2,363 71,359 55,736 49,489 5,058 7,742 187 3,422 1,497 1,259 NA NA NA 83,Complex NA NA NA NA NA NA NA NA NA NA NA NA 42,180 29,272 35,753 42,Totals 40,530 31,054 22,463 102,948 84,725 67,803 7,324 14,720 390 5,153 3,268 2,283 42,180 29,272 35,753 198,

Table 7. Thermoelectric plant water consumption by generation and cooling-system types as reported to the U.S. Department of Energy, Energy Info(EIA) for 2005 and 2010, and as modeled by the U.S. Geological Survey (USGS) for 2010. [Values may not sum to totals because of independent rounding. All consumption is in millions of gallons per day; NGCC, natural gas combined cycle; NR, not reported; NC, noComplex, geothermal and solar thermal plants and plants that have multiple cooling-system types, generation technologies, and/or use multiple fuels] Genera- tion type Cooling-system type 

Once-through saline Once-through fresh Recirculating pond Recirculating tower Complex EIA USGS EIA USGS EIA USGS EIA USGS EIA USGS 

2005 2010 2010 2005 2010 2010 2005 2010 2010 2005 2010 2010 2005 2010 2010 

Oil NR NR NC NR 25 0.2 NR NR NA 12 0.4 0.8 NA NA NA Nuclear NR NR NC 219 236 157 168 64 166 414 384 433 NA NA NA NGCC NR 15 NC NR 0.3 5 7 0.2 16 600 334 268 NA NA NA Gas steam NR 38 NC 28 30 27 103 3 21 62 42 23 NA NA NA Coal NR NR NC 210 288 503 183 370 187 2,164 835 867 NA NA NA Complex NR NA NA NA NA NA NA NA NA NA NA NA 793 603 832 Totals NR 53 NC 456 579 692 462 437 390 3,251 1,596 1,591 793 603 832 
Results and Discussion 15

Table 8. Thermoelectric water-withdrawal coefficients calculated from flow rates and net electrical generation as reported to the U.S. 

Department of Energy, Energy Information Administration (EIA) and as calculated from modeled estimates by the U.S. Geological Survey 

(USGS) for 2010.

[All coefficients are in gallons per killowatt hour; NGCC, natural gas combined cycle; NR, not reported; NA, not applicable]

Generation 

type

Cooling-system type

Once-through saline Once-through fresh Recirculating pond Recirculating tower

EIA USGS EIA USGS EIA USGS EIA USGS

2005 2010 2010 2005 2010 2010 2005 2010 2010 2005 2010 2010

Oil 78 101 47 71 177 56 NR NR NA 12.75 1.6 0.99

Nuclear NR 28 39 NR 37 39 NR 22.24 0.78 NR 1.44 0.81

NGCC NR 15 14 209 26 11 0.59 7.78 0.35 2.61 0.54 0.29

Gas steam 343 339 38 209 107 39 41.95 75.87 2.19 2.32 1.45 0.82

Coal 44 59 32 40 37 32 14.46 23.01 0.65 1.84 0.75 0.63

Table 9. Thermoelectric water-consumption coefficients calculated from flow rates and net electrical generation as reported to the 

U.S. Department of Energy, Energy Information Administration (EIA) and as calculated from modeled estimates by the U.S. Geological 

Survey (USGS) for 2010.

[All coefficients are in gallons per killowatt hour; NGCC, natural gas combined cycle; NR, not reported; NC, not calculated; NA, not applicable]

Generation 

type

Cooling-system type

Once-through saline Once-through fresh Recirculating pond Recirculating tower

EIA USGS EIA USGS EIA USGS EIA USGS

2005 2010 2010 2005 2010 2010 2005 2010 2010 2005 2010 2010

Oil NR NR NC NR 125.33 0.59 NR NR NA 12.21 0.71 0.70

Nuclear NR NR NC NR 0.4 0.4 NR 0.27 0.78 NR 0.51 0.58

NGCC NR 0.16 NC NR 0.01 0.12 0.26 0.02 0.35 1.51 0.28 0.20

Gas steam NR 1.22 NC 0.59 0.54 0.44 4.03 0.13 2.19 1.4 1.22 0.58

Coal NR NR NC 0.12 0.19 0.33 0.52 1.1 0.65 1.17 0.42 0.43

Total EIA-reported consumption declined 1.7 Bgal/d 

from 2005 to 2010 (table 7), a 34-percent decrease. Reported 

consumption for plants with tower cooling systems declined 

for all generation types (fig. 7), with a 61-percent decrease 

at coal-fired plants. The reduction in consumption at cooling 

towers is hard to reconcile with (1) the increased share of net 

electrical generation for plants with tower cooling systems 

(fig. 6; table 3), (2) a 33-percent increase from 2005 to 2010 in 

the number of tower plants that reported water use to the EIA 

(U.S. Department of Energy, Energy Information Administration, 2006b and 2011b), and (3) the relatively large volumes 

of water consumed through evaporation associated with tower 

cooling technology (Macknick and others, 2011). Similarly, 

reported consumption for once-through freshwater cooling 

systems increased while net generation decreased (figs. 6 

and 7; tables 3 and 7). 

Withdrawal and consumption coefficients computed 

based on EIA-reported information (tables 8 and 9) vary considerably among plant categories and reporting years; of the 

23 pairs of coefficients that can be compared between 2005 

and 2010, 12 increased or decreased by more than a factor 

of 2. As noted earlier, reported withdrawals declined for simple plants from 2005 to 2010 while net generation increased 

overall, and nearly all decreases in withdrawal for individual 

categories were reflected in a decrease in the withdrawal coefficient for that category (tables 6 and 8). 

Most of the decline in consumption at simple plants was at 

coal plants with recirculating towers, and was associated with 

an unexplained 64-percent decrease in the consumption coefficient for these plants (table 9). The decrease in the consumption 

coefficient for coal plants with towers was intermediate between

larger decreases for oil and NGCC plants, and smaller decreases 

for nuclear and gas steam plants. Similar to the USGS-modeled 

coefficients discussed above, several consumption coefficients 

derived from EIA-reported data for both 2005 and 2010 lie 

outside the ranges reported by Macknick and others (2011). 

Large changes in withdrawal and consumption coefficients between 2005 and 2010 were the rule rather than the 

exception. Such changes are physically possible with great 

increases or decreases in the thermal efficiency of generation 
16 Withdrawal and Consumption of Water by Thermoelectric Power Plants in the United States, 2010

0

 10

 20

 30

 40

 50

 60

 70

 80

 90

 100

 110

Withdrawal, billions of gallons per day

Figure 5

2005

2010

Once-through

saline

Once-through

fresh

Recirculating

pond

Towers

Oil

Nuclear

NGCC

Gas steam

Coal

Generation type

EXPLANATION

Figure 5. Water withdrawal 

by generation type and 

cooling-system type for simple 

thermoelectric power plants, 

2005 and 2010. [Data reported 

to the U.S. Department of 

Energy, Energy Information 

Administration; NGCC, natural 

gas combined cycle]

0

 100

 200

 300

 400

 500

 600

 700

 800

 900

 1,000

 1,100

 1,200

 1,300

 1,400

 1,500

Once-through

saline

Once-through

fresh

Recirculating

pond

Towers

Net generation, billions of kilowatt hours

2005

2010

Oil

Nuclear

NGCC

Gas steam

Coal

Generation type

EXPLANATION

Figure 6. Net electrical 

generation by generation type 

and cooling-system type for 

simple thermoelectric power 

plants, 2005 and 2010. [Data 

reported to the U.S. Department 

of Energy, Energy Information 

Administration; NGCC, natural 

gas combined cycle]
Results and Discussion 17

or the water efficiency of cooling systems. However, most of 

the technology involved in thermoelectric water use is mature, 

and efficiency changes only gradually as new plants and 

cooling systems replace old ones within each plant category. 

Overall, the best explanation for the changing coefficients 

from 2005 to 2010 may not be technological factors, but rather 

changes in definitions and reporting practices. 

Alternative Water

Alternative water use has potential to offset withdrawal 

and consumption of water otherwise suited to meet a broad 

range of socioeconomic and environmental uses. Unfortunately the assessment of that potential requires addressing a 

number of definitional issues. For example, EIA survey forms 

recognize five distinct water types (table 5) but do not include 

definitions, leaving coding to the interpretation of plant operators. The USGS defines “saline water” as water having dissolved-solids concentrations too high for human consumption 

or irrigation, with a lower threshold of 1,000 milligrams per 

liter (mg/L)—about 1/35 the salinity of seawater (U.S. Geological Survey, 2013), likely including most or all water 

reported by the EIA as “brackish.” The EIA reports consumption of saline and brackish water, whereas the USGS generally 

regards evaporation of such water as a negligible component 

of global and national water budgets and does not estimate 

such consumption. The EIA reports delivery of water from 

a treatment plant to a power plant as a withdrawal, but such 

delivery does not meet the USGS definition of withdrawal 

as coming from a natural hydrologic system. To facilitate 

comparison of EIA-reported and USGS-estimated alternative 

water use, the EIA usage for withdrawal and consumption is 

used in this section.

EIA-reported and USGS-estimated alternative-water 

withdrawals for 2010 were about 40 and 30 Bgal/d, respectively (fig. 8). These withdrawals represent about one-quarter 

of the respective national totals for reported and estimated 

thermoelectric withdrawals (table 6). Saline and brackish water types constitute about 95 percent of EIA-reported 

withdrawal, and saline water type is about 98 percent of 

USGS-estimated withdrawals (fig. 8). More than 95 percent 

of reported or estimated saline or brackish withdrawals were 

taken from surface-water sources for once-through cooling 

systems (appendix 1). Reclaimed wastewater, such as treated 

sewage effluent, is less than 1 percent of alternative water 

withdrawals and about a third of that use is at one plant, Palo 

Verde in Arizona (appendix 1). 

In comparison to withdrawals, alternative-water consumption was relatively small in 2010. Reported and estimated 

alternative-water consumption, 294 and 169 Mgal/d, respectively (fig. 9), represents less than 1 percent of alternativewater withdrawals and less than 10 percent of national total 

consumption (figs. 8 and 9; table 7). 

Figure 7

Once-through

saline

Once-through

fresh

Recirculating

pond

Towers

Consumption, in millions of gallons per day

2005

2010

Oil

Nuclear

NGCC

Gas steam

Coal

Generation type

EXPLANATION

0

 500

 1,000

 1,500

 2,000

 2,500

 3,000

 3,500

Figure 7. Water consumption 

by generation type and 

cooling-system type for simple 

thermoelectric power plants, 

2005 and 2010. [Data reported 

to the U.S. Department of 

Energy, Energy Information 

Administration; NGCC, natural 

gas combined cycle]
18 Withdrawal and Consumption of Water by Thermoelectric Power Plants in the United States, 2010

EIA = 40 Bgal/d

12

25

1.3

0.2

USGS = 30 Bgal/d

Note: Units are in

billion gallons per day

(Bgal/d)

0.3

29.7

0.2 1.3

Figure 8.

Reclaimed

Fresh/brackish

Brackish

Saline

Other

EXPLANATION

A B

Figure 8. Alternative water withdrawals by thermoelectric plants in the United States as (A) reported to the U.S. Department 

of Energy, Energy Information Administration (EIA), and (B) estimated by the U.S. Geological Survey (USGS), 2010.

EIA = 294 Mgal/d USGS = 169 Mgal/d

A B

75

154

40

19

6

143

26

Note: Units are in

million gallons per day

(Mgal/d)

Reclaimed

Fresh/brackish

Brackish

Saline

Other

EXPLANATION

Figure 9.

Figure 9. Alternative water consumption by thermoelectric plants in the United States as (A) reported to the U.S. Department 

of Energy, Energy Information Administration (EIA), and (B) estimated by the U.S. Geological Survey (USGS), 2010.
Results and Discussion 19

The most striking difference between alternative-water 

withdrawal and consumption is in the relative contributions 

of different water types. Reclaimed water represents 1 percent 

or less of reported and estimated alternative water withdrawal 

but 52 and 85 percent of respective consumption (fig. 9). This 

inversion of the relative importance of reclaimed water largely 

reflects uneven reporting of consumption as it applies to saline 

and brackish waters. Of 104 plants reporting withdrawal of 

such water to the EIA, only 26 plants reported consumption, 

while the USGS did not estimate consumption for any plants 

reporting saline or brackish water types. If saline and brackish water types are ignored, reported and estimated alternative 

water consumption numbers conform fairly well, totaling to 

173 and 169 Mgal/d, respectively (fig. 9). Almost all of the 

plants using reclaimed wastewater use recirculating towers for 

cooling (appendix 1).

Comparison of EIA 2010 Data to USGS 

Model Results 

The national withdrawal estimated from heat-budget 

models for 2010 was about 21 percent lower than the withdrawal based on EIA-reported data; in contrast, the modelbased consumption total was about 9 percent higher than the 

EIA-based total consumption. Differences between reported 

and estimated totals are inconsistent among individual plant 

categories. As an example, estimated withdrawal was 38 percent more than reported withdrawal for once-through saline 

simple nuclear plants, whereas estimated withdrawal was 29 to 

97 percent less than reported withdrawal for other cooling 

types (table 6). 

Comparison with heat-budget model results identified 

a few plants with reported withdrawals too high to be easily explained thermodynamically; these relatively few plants 

contributed most of the difference between national totals 

for reported and estimated withdrawal. Differences between 

USGS- and EIA-based coefficients reflect differences in 

definitions, difficulties in measuring, and possibly errors in 

reported information. Improved information from just a few 

plants might greatly increase the accuracy of coefficients and 

aggregate values calculated from EIA-reported information. 

Of the 1,290 plants for which withdrawals were modeled, 736 reported non-zero withdrawal to the EIA. These 

736 plants produced 88 percent of the total net generation 

at the 1,290 plants, of which only two-thirds was produced 

by plants reporting withdrawals within the minimum and 

maximum of estimated withdrawals. At 132 plants, representing 13 percent of the total net generation at the 1,290 plants, 

EIA-reported withdrawals were higher than the maximum 

thermodynamically plausible values based on heat-budget 

models. Reported withdrawals at these plants were about 

25 Bgal/d, while modeled best estimates totaled 1 Bgal/d and 

maximum withdrawals with margins of uncertainty totaled 

about 3 Bgal/d. The excess of reported withdrawals of about 

22 Bgal/d above maximum modeled estimates is difficult to 

reconcile with heat budgets, even with compensating assumptions. Of this excess, 32 percent is reported from a single 

plant, El Segundo Power in Los Angeles (appendix 1) and 

an additional 48 percent is associated with 9 other plants. 

Together these 10 plants represent more than half of the difference between EIA-reported withdrawal and USGS-estimates, 

and their total reported withdrawal was 32 times larger than 

the total of USGS-estimated maximum withdrawal for the 

same plants.

Coefficients based on withdrawals reported to EIA were 

higher than withdrawal coefficients estimated from heatand water-budget models for several plant types (table 8). 

Reported withdrawal at recirculating ponds exceeded estimated withdrawal across all generation types, reflecting 

similar differences in withdrawal coefficients. Some large 

withdrawals reported to the EIA for recirculating ponds appear 

to be flows through condensers rather than makeup flows to 

ponds. Currently, EIA form 923 allows reporting such flows 

as withdrawal at recirculating ponds, and the values reported 

are large enough to support this inference. Because the USGS 

defines withdrawal as water taken from a natural hydrologic 

system, only makeup flow is included in USGS-modeled 

coefficients. As a result, USGS withdrawal coefficients for 

recirculating ponds are predictably lower than those based on 

EIA-reported withdrawals. 

Based on comparison to USGS estimates, most thermoelectric generation in 2010 is not associated with thermodynamically plausible EIA-reported values of both withdrawal 

and consumption. Those plants reporting values greater than 

zero to EIA contributed 70 percent of 2010 net generation, 

and those also reporting values between modeled minima 

and maxima contributed only 33 percent of net generation for 

plants with estimated consumption (appendix 1). Likewise, 

those plants reporting non-zero values for both withdrawal 

and consumption contributed 69 percent of net generation 

and those also reporting values between modeled minima 

and maxima contributed only 25 percent of net generation for 

plants with estimated consumption (appendix 1). 

 Consumption coefficients based on EIA data for recirculating ponds were low relative to USGS estimates for the same 

plant types, except for coal-fired plants (table 9). Estimated 

consumption coefficients for recirculating ponds were higher 

than those for towers within each generation type. In contrast, 

coefficients computed from EIA-reported consumption were 

lower for recirculating ponds than for towers for all generation 

types other than coal-fired plants. 

For once-through consumption, differences between 

USGS-estimated and EIA-based coefficients were inconsistent, reflecting the lack of a single recommended method for 

estimating such consumption for reporting to the EIA. Consumption coefficients for towers were in general agreement 

between EIA-reported data and the USGS models, except 

at gas-fired steam plants where the EIA-based coefficient is 

higher than the model-based coefficient (table 9). 
20 Withdrawal and Consumption of Water by Thermoelectric Power Plants in the United States, 2010

Even though large differences exist within plant categories, the total EIA-reported consumption was only 8 percent 

less than that estimated from heat- and water-budget models 

(table 7). Reported consumption was lower than estimated 

consumption for once-through cooling systems and for all 

towers except those at gas-fired plants. Definitional differences, measurement difficulties, and reporting practices may 

all contribute to these differences.

Conclusions

The heat-budget approach offers a new perspective on 

estimating thermoelectric water use. Models of heat and water 

flows in power plants are based on simplifying assumptions 

about plant technology and evaporation processes. Although 

these models rely on information about plant technology, 

fuel use, and electric generation reported to the U.S. Department of Energy, Energy Information Administration (EIA), 

they provide independent estimates of water use. The models 

used in this investigation produced average withdrawal and 

consumption coefficients that are inconsistent with previously 

published values for several combinations of generation technology and cooling type, expanding the already broad range of 

estimated coefficients for several plant types. 

Examination of EIA data for simple plants shows that water 

withdrawals declined considerably from 2005 to 2010. Most 

of the decline can be attributed to coal-fired plants with oncethrough cooling systems. The data also indicate that the share of 

net electrical generation increased at plants using recirculating 

towers for cooling, the largest increase occurring at natural gas 

combined cycle plants. These findings may reflect conversion 

from once-through to recirculating-tower cooling, and new, 

more efficient plants using tower cooling coming online.

Although reported and modeled withdrawals of alternative 

water types are somewhat inconsistent, both indicate that most 

alternative water withdrawals are seawater and tidal brackish 

water for once-through cooling. Reclaimed wastewater, such 

as treated sewage effluent, is less than 1 percent of alternative 

water withdrawals and about a third of that use is at one plant. 

Consumption and withdrawal coefficients based on 

reported water use show inconsistent results between years, 

among plant categories, and with values in the published literature. Changes to the EIA forms in 2010 may have contributed 

to the inconsistencies between 2005 and 2010 results. 

Heat-budget models produced a lower estimate of 

national total thermoelectric withdrawal and a higher estimate 

of consumption than EIA-reported values. Most thermoelectric 

generation in 2010 is not associated with thermodynamically 

plausible EIA-reported values of both withdrawal and consumption. Ratios of reported to modeled values at individual 

plants vary widely. 

Uncertainties can be reduced by improvements in 

measuring and reporting water flows at plants, refinements in 

modeling evaporation and withdrawal, and improved environmental data collection at thermoelectric plants. In particular, 

consumption by once-through systems cannot be measured 

directly, and modeling such consumption would benefit from 

better information on surface-water temperatures.

In principle, both the heat budget approach and the practice of reporting withdrawal and consumption are valid ways to 

estimate thermoelectric water use, but both methods need to be 

refined. Inconsistencies in results suggest that actual uncertainty 

in thermoelectric water use is on the order of 10 to 20 percent 

or more for national totals and much more for individual plants. 

Examination of the differences among various coefficients that 

represent the same flow at the same type of plant may illuminate methodological issues that need to be resolved in order to 

improve estimates of thermoelectric water use.
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Glossary 27

A

alternative water Water used at thermoelectric power plants as an alternative to 

freshwater; includes reclaimed water such as 

treated effluent from sewage treatment plants, 

groundwater that is unsuitable for drinking or 

irrigation because it is high in salts or other 

impurities, and seawater.

B

blowdown Water discharged from the 

cooling system to dispose of accumulating 

dissolved solids.

boiler efficiency The ratio between the 

amount of heat used to generate steam and the 

total heat content of the fuel that is consumed.

brackish water Water with a dissolvedsolids concentration between 1,000 and 

10,000 milligrams per liter.

C

capacity factor The total power produced in 

a given period divided by the product of the 

net unit capacity and the given time period.

condenser duty The amount of waste heat 

delivered to the cooling system through the 

condenser.

condenser range The increase in cooling 

water temperature as it passes through the 

condenser.

cooling system A system that removes 

waste heat from a power plant condenser and 

transfers it to the atmosphere.

cooling-system type The technology used to 

dissipate condenser duty to the atmosphere.

cycles of concentration The ratio of dissolved solids in the [circulating and] blowdown 

water to dissolved solids in the makeup water.

D

design range The condenser range under 

design conditions, i.e., with the plant running 

at full power.

dry cooling system A cooling system that condenses steam and transfers the waste heat to the 

atmosphere without the consumption of water.

E

evaporation ratio The ratio of the amount of 

heat transferred to the air as evaporation to the 

condenser duty.

F

forced evaporation The increase in evaporation of surface water due to the added heat of 

discharged cooling water.

freshwater Water that contains less than 

1,000 milligrams per liter of dissolved solids.

G

generation type The type of technology 

used to generate electricity in a given unit or 

plant, including the energy source and prime 

mover.

H

heat budget A summation of all significant 

flows of heat into and out of a system such as 

a power plant.

high range As applied to condensers, having 

a condenser range greater than 25 degrees 

Fahrenheit (°F).

L

linked heat and water budget A summation 

of all significant flows of heat and water into 

and out of a power plant, linked by converting energy flows embodied in water flow and 

evaporation into their equivalent volume flow 

rates of liquid water.

M

makeup Water added to the cooling system 

to replace evaporation and blowdown.

medium range As applied to condensers, 

having a condenser range between 10 and 

25 degrees Fahrenheit (°F).

N

natural evaporation In contrast to forced 

evaporation, the evaporation of surface water 

due to heat from sources other than the power 

plant. 

Glossary
28 Withdrawal and Consumption of Water by Thermoelectric Power Plants in the United States, 2010

net generation The amount of electricity 

generated by a power plant and transmitted. 

Net generation is the gross electrical energy 

generated minus electrical energy consumed 

in the plant by auxiliary equipment.

O

once-through cooling system A cooling system in which the water is withdrawn from a 

surface-water source other than a recirculating 

pond to condense the steam used to generate 

electricity and that discharges the water back 

to surface water at a higher temperature.

P

plant A facility that generates electricity 

from another source of energy such as fossil 

fuels, nuclear fission, geothermal energy, or 

solar radiation and heat.

prime mover In thermoelectric plants, the 

prime mover is the turbine that converts the 

energy in heated gases to mechanical energy.

pumpage As applied to cooling systems, the 

amount of water moved by pumps.

R

recirculating cooling system A cooling 

system in which water is circulated through 

condensers, cooled, and then re-used in the 

same process.

S

saline water Water that contains 1,000 milligrams per liter or more of dissolved solids.

surface-water cooling system A coolingsystem type that transfers heat from a condenser to the atmosphere through evaporation 

at the free surface of an open body of water. In 

addition to evaporation, some heat leaves the 

water surface through conduction and radiation.

T

thermal efficiency The percentage of fuel 

heat used to produce electricity.

thermoelectric Relating to the generation of 

electric power from heat.

thermoelectric water consumption The 

water evaporated or incorporated into byproducts as a result of the production of electricity 

from heat.

thermoelectric water withdrawal The water 

removed from groundwater or surface water 

for use in a thermoelectric power plant.

W

waste heat Heat used but not converted to 

electricity in a thermoelectric plant.

water budget A summation of all significant 

flows of water into and out of a system such 

as a power plant.

wet cooling tower A cooling-system type 

that transfers heat from a condenser to the 

atmosphere primarily through evaporation, 

and to a lesser extent through conduction, in a 

natural-draft or mechanical-draft tower.

For additional information, contact:

Eric J. Evenson

Coordinator—National Water Census

U.S. Geological Survey

3450 Princeton Pike, Suite 110

Lawrenceville, NJ 08648

or visit the National Water Census Web site at 

http://water.usgs.gov/watercensus

Prepared by:

USGS Science Publishing Network

Raleigh Publishing Service Center

3916 Sunset Ridge Road

Raleigh, NC 27607

Diehl and Harris—Withdrawal and Consumption of Water by Thermoelectric Power Plants in the United States, 2010—Scientific Investigations Report 2014–5184

Printed on recycled paper

ISSN 2328-0328 (online)

ISSN 2328-031X (print)

http://dx.doi.org/10.3133/sir20145184