Freshwater Use by U.S. Power Plants: 

Electricity’s Thirst for a Precious Resource

Glossary and Acronyms

Acre-foot A volume equal to 325,851 gallons.

Air cooling See dry cooling.

Basin An area where elevation changes allow rainwater and surface water to gather 

into streams that flow to a common outlet point. See also sub-basin.

Carbon intensity The amount of carbon dioxide emitted per unit of electricity generated.

Consumption The amount of water lost to evaporation at a power plant during the cooling 

process.

Cooling pond An onsite reservoir where a power plant stores water for cooling.

Cooling tower A structure that uses cools water heated during the thermoelectric steam cooling 

process to allow the water to be reused for cooling.

Dry cooling A cooling system that blows air across steam-carrying pipes to cool them, rather 

than using water.

East of the 

Mississippi

For purposes of this analysis, includes Alabama, Connecticut, Delaware, Florida, 

Georgia, Illinois, Indiana, Kentucky, Massachusetts, Maryland, Maine, 

Michigan, Mississippi, North Carolina, New Hampshire, New Jersey, New York, 

Ohio, Pennsylvania, Rhode Island, South Carolina, Tennessee, Virginia, 

Vermont, Wisconsin, and West Virginia.

Entrainment The act of pulling larval fish or eggs through a power plant cooling system.

Freshwater In this analysis, all non-ocean sources of water. 

Generator A turbine that turns physical energy into electrical energy. A single power plant 

may have several generators. 

Hybrid cooling A cooling system that uses dry cooling most of the time, but that can draw on 

water for cooling during hot periods.

Hydrologic unit 

code (HUC)

Numbers used by the U.S. Geological Survey (USGS) to identify all the basins 

in the United States (see basin). A 2-digit HUC is used to identify the 21 largest 

basins. An 8-digit HUC is used to identify the smallest sub-basins (see subbasin), which are within the 2-digit HUCs. The first two numbers in each 8-digit 

HUC indicate the larger 2-digit HUC basin. 

Impingement The trapping of fish against a screen during a power plant’s intake of cooling 

water. This injures or kills the fish.

Natural gas 

combined-cycle

A power plant that burns natural gas to generate hot gases, which are used to turn 

a turbine to generate electricity. The plant then uses the hot gases to make steam 

to drive another electricity-generating turbine.

Once-through 

cooling

A cooling system that withdraws water from nearby sources and passes it 

through pipes to absorb heat from steam, before releasing the water back to the 

source.

Organic fuels Coal, oil, natural gas, and biomass, as specified in the definition of organic fuels 

on EIA forms 860 and 923.

Recirculating 

cooling

A cooling system that withdraws water and uses it several times for cooling 

steam before releasing the water back to the source or evaporating it completely.

Renewable 

energy

In this analysis, includes biomass, geothermal, hydroelectric, solar, and wind.

Southeast In this analysis, states that are part of the South Atlantic Basin: Alabama, 
Freshwater Use by U.S. Power Plants: Electricity’s Thirst for a Precious Resource

Glossary and Acronyms

Florida, Georgia, Louisiana, Mississippi, North Carolina, South Carolina, 

Tennessee, and Virginia.

Southwest In this analysis, states that are part of the Upper or Lower Colorado Basin: 

Arizona, California, Colorado, Nevada, New Mexico, Utah, and Wyoming.

Sub-basin Part of a basin, where rain and surface water into streams, often flowing to a 

common outlet point where they join a larger flow. 

Thermoelectric Power plants that boil water to create steam, which drives turbines to produce 

electricity. This process is also called steam generation. Thermoelectric power 

plants include all coal, nuclear, oil, biomass, geothermal, and steam-producing 

concentrating solar plants, and most natural gas plants. Wind turbines, solar 

photovoltaic generators, non-steam concentrating solar power technologies, and 

natural gas combustion turbines are not thermoelectric plants.

Water intensity The amount of water power plants use—that is, withdraw and consume—per 

unit of electricity generated.

West of the 

Mississippi

In this analysis, includes Alaska, Arizona, Arkansas, California, Colorado, 

Hawaii, Idaho, Iowa, Kansas, Louisiana, Minnesota, Missouri, Montana, 

Nebraska, New Mexico, Nevada, North Dakota, Oklahoma, Oregon, South 

Dakota, Texas, Utah, Washington, and Wyoming.

Withdrawal The total amount of water a power plant takes in from a source such as a river, 

lake, or aquifer, some of which it returns.

Acronyms and Abbreviations

CO2 Carbon dioxide

EIA Energy Information Administration

EW3 Energy and Water in a Warming World initiative

HUC Hydrologic unit code (see Glossary)

kWh Kilowatt-hour

MGD Million gallons per day

MWh Megawatt-hour

NREL National Renewable Energy Laboratory 

UCS Union of Concerned Scientist

USGS U.S. Geological Survey

WaSSI Water Supply Stress Index (see Appendix A)