Conventional Power Plants: Water withdrawal versus consumption
According the US Geological Survey (USGS), production of electrical power results in one of the largest uses of water in the United States and worldwide. In 2005, about 201,000 million gallons of water each day were used to produce electricity (excluding hydroelectric power) and surface water accounted for more than 99 percent of total thermoelectric-power withdrawals. While some of the water withdrawn provides water to drive the steam turbines and generate electricity, much of the water is used for cooling the power-producing equipment.
When evaluating water use by thermoelectric-power plants, a distinction needs to be made between that of water withdrawal and water consumption. Water withdrawal entails the removal of water from a local water source; the withdrawn water may or may not get returned to its source or made available for use elsewhere. Water consumption refers to the use of water in such a way as to prohibit it being returned to its source, usually because it is lost to evaporation. While water withdrawal by conventional power plants can be high, consumption can be low if the withdrawn water is returned to lakes and streams. In 2005, withdrawal of water by thermoelectric power plants for cooling represented 44% of water withdrawn nationally, and 6% of water consumed (Congressional Research Service, 2010).
Droughts and hot summers can influence water withdrawals by power plants as they adjust to low water supply levels and/or use warmer water for their cooling operations; a graphic from the Union of Concerned scientists (UCS) illustrating these scenarios is available. And for power plants that return water to its source, the returned water, now warmer, can impact the aquatic ecosystem in which it is discharged, which is referred to as thermal pollution. Another graphic from the UCS indicates regions around the country that have encountered power production/water supply issues associated with hotter and drier summers.
To learn more about cooling water, cooling water systems at power plants and thermal pollution, the following resources may be helpful:
Thermoelectric Power Water Use, USGS. This website includes graphics and a schematic of a coal-fired power plant that relies on a closed-loop cooling system.
Thermal pollution, Encyclopedia of Earth. This website includes satellite image illustrating thermal pollution in association with a power plant.
Cooling water for energy generation and its impact on national-level water statistics, Food and Agriculture Organization of the United Nations, 2011 (pdf). This document includes graphics depicting once-through and closed-loop cooling systems, comparison of withdrawal and consumption for each type of system.
Energy’s Water Demand: Trends, Vulnerabilities, and Management, Congressional Research Service, 2010 (pdf).
Energy-water collision, Union of Concerned Scientists. This website includes graphics and links to supporting scientific publications.