How it Works: Water for Electricity

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Article courtesy of Union of Concerned Scientists | July 15, 2013 | Shared as educational material

How Water Used to Generate Electricity

The United States uses many different technologies to produce electricity.  It is important to understand the different impacts these technologies have on water resources.   

1. Water’s Many Roles in Electricity
2. Generating Electricity Requires Substantial Amounts of Water
3. Electricity Can Also Affect Water Quality

Water’s Many Roles in Electricity

Water is involved at many points in the process of producing electricity:

  • Electricity Generation – More than 90 percent of U.S. power plants need cooling. These types of power plants are called thermoelectric because they use a heat source to produce steam for generating electricity. Hydroelectric power plants use water in a different way, converting the energy in falling water into electricity by passing it through turbines.
  • Fuel Extraction and Production – Water is a critical resource for the drilling and mining of natural gas, coal, oil, and uranium. In many cases, fuel extraction also produces wastewater, as with natural gas and oil wells and coal slurry ponds.
  • Fuel Refining and Processing – Oil, uranium, and natural gas all require refining before they can be used as fuels – a process that uses substantial amounts of water.
  • Fuel Transportation – Water is used to transport coal through slurries — pipelines of finely ground coal mixed with water — and to test energy pipelines for leaks.[1]
  • Emissions Control – Many thermoelectric power plants emit sulfur, mercury, particulates, carbon dioxide, and other pollutants, and require pollution control technologies. These technologies also require significant amounts of water to operate.

Generating Electricity Requires Substantial Amounts of Water

Water use in power plants has two components: withdrawal and consumption. Water withdrawal is the act of removing water from a local water source; the withdrawn water may or may not get returned to its source or made available for use elsewhere.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 is the use of water in a power plant in a way such that the water is not returned, usually because it is lost to evaporation.

Some power plants use cooling systems that draw water from a lake, river, aquifer, or ocean to cool steam and then return virtually all of it — although at higher temperatures — to the source. Such systems, known as once-through cooling systems, have high withdrawals but low consumption. Coal and nuclear plants, for example, may draw 20 to 60 gallons of water for every kilowatt-hour of electricity they produce, depending on how they are cooled. [2]  Largely because of older power plants using this approach, electric power generation is responsible for more than 40 percent of freshwater withdrawals in the United States — on the order of 100 billion gallons per day in 2008 — primarily for cooling.[3]

Water withdrawal by power plants can become a major challenge during times of drought or other water stress, when water is simply not available in the required volumes or at the required temperatures. Drawing vast volumes of cooling water through systems of pumps and pipes can also trap and kill fish, insect larvae, and other organisms.

Power plants using other cooling systems, known as recirculating or closed-loop systems, withdraw only a fraction of the amount that once-through systems do, but consume most or all of it. Power plant water consumption becomes a large problem in water constrained regions where competition among users is high. Hydropower plants withdraw large amounts of water to run through their turbines, while the lakes they rely on can also consume water quickly by evaporation; however, dammed lakes are used for multiple purposes, such as agricultural irrigation, flood control, and recreation.  Hydropower does not account for all of this water usage.

Electricity Can Also Affect Water Quality

Producing electricity can have significant implications for water quality.  For example:

  • Water used to cool electricity-generating steam exits the power plant at substantially higher temperatures — up to 18º F hotter at power plants in summer. [4] This “thermal pollution” can harm local aquatic ecosystems, especially during the summer months when species are at or near their heat tolerance thresholds.
  • Minerals unearthed during fuel mining and drilling can contaminate groundwater, which in turn affects drinking water and local ecosystems.
  • Coal mining and combustion create wastes with dangerous toxins such as mercury, lead, and arsenic; and improper storage or disposal of those wastes can contaminate water supplies.  Coal combustion can also create acid rain, increasing the acidity of lakes and streams and harm aquatic ecosystems.   

[1] US Department of Energy (DOE). 2006. Energy Demands on Water Resources: Report to Congress on the Interdependency of Energy and Water. Washington, DC.
[2] J. Macknick, R. Newmark, G. Heath, and K.C. Hallet. 2012. Operational water consumption and withdrawal factors for electricity generating technologies: a review of existing literature. Environmental Research Letters. 7 doi:10.1088/1748-9326/7/4/045802.
[3] K. Averyt, J. Fisher, A. Huber-Lee, A. Lewis, J. Macknick, N. Madden, J. Rogers, and S. Tellinghuisen. 2011. Freshwater use by U.S. power plants: Electricity’s thirst for a precious resource. A report of the Energy and Water in a Warming World Initiative. Cambridge, MA: Union of Concerned Scientists. November.
[4] N. Madden, A. Lewis, and M. Davis. 2013. Thermal effluent from the power sector: ananalysis of once-through cooling system impacts on surface water temperature. Environmental Research Letters. 8 doi:10.1088/1748-9326/8/3/035006.


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