What Are the Differences in Water Usage between Various Energy Technologies?

Ask a Scientist - December 2011

K. French, of North Charleston, SC asks: Lots of different inputs are involved when we talk about producing electricity sustainably. Along these lines, what can you tell me about differences in water usage between various energy technologies like solar, wind, coal, and natural gas?” She is answered by John Rogers, Senior Analyst in the Climate and Energy Program.

Thank you for your question. As you suggest, water usage and energy production are intertwined in many ways. The first thing to note is simply how much water electric power plants currently withdraw from our nation’s rivers, lakes, groundwater aquifers, and oceans. Power plants withdraw as much water as all U.S. farmers do to irrigate the nation’s crops, and four times more than all U.S. residential uses combined—including everything from drinking and washing dishes to flushing toilets and watering lawns.

Power plants withdraw that enormous volume of water—on the order of a hundred billion gallons of freshwater alone each day—because the vast majority of power plants in the United States use steam to drive turbines that generate electricity, and water to cool that steam for re-use. The steam might be created by burning fossil fuels, from the heat generated by a nuclear reaction, or even from renewable energy options such as biomass, geothermal, and concentrating solar power plants. Ninety percent of the electricity we use comes from plants that use steam, and steam cooling accounts for the overwhelming majority of the water that most power plants use.

The Union of Concerned Scientists, working with a team of independent experts from around the country, just issued the nation’s first comprehensive report on power plant water use and related water stress. In our research, we looked at both water withdrawals—how much plants take out of rivers, lakes, or aquifers—and water consumption—how much they evaporate as part of the cooling process. Overall, our research found that by far the largest water users by type are coal-fired plants, which are still the dominant source of electricity in the United States. Coal plants accounted for 67 percent of all freshwater withdrawals for thermoelectric power plants in 2008, and 65 percent of consumption. Nuclear plants, meanwhile, accounted for 27 percent of power plant freshwater withdrawals and 24 percent of consumption. Comparatively, the nation’s natural gas fleet generates considerably more power for each drop of water it uses. While gas-fired plants produce some 18 percent of the nation’s freshwater-cooled thermoelectric power, they account for just 4 percent of withdrawals of freshwater and 9 percent of consumption.

As the above numbers on nuclear suggest, low-carbon electric technologies are not necessarily low-water. According to our analysis, our nation’s nuclear plant fleet as a whole withdrew eight times as much freshwater in 2008 as our natural gas fleet per unit of electricity generated. Some renewable energy options can also have water implications. Some of the nation’s wet-cooled concentrating solar power plants, for example, consume more water per unit of electricity than the average coal plant. It is important to note, though, that other renewable energy options, including wind turbines and solar photovoltaic panels, create electricity with no water involved whatsoever. 

As your question suggests, different electricity options involve different inputs at many stages, and that is certainly true for water; water use for electricity doesn’t start or stop with power plant cooling. Water is involved in manufacturing the materials that go into making any power plant.  Fuel extraction and refining, especially for coal and nuclear, often have significant impacts on water quantity and quality. For example, U.S. coal mining uses 70 million to 260 million gallons of water each day, according to the Department of Energy. Mountaintop removal mining of coal has buried almost 2,000 miles of Appalachian headwater streams—some of the most biologically diverse streams in the country, according to the Environmental Protection Agency. Uranium mining for nuclear fuel has contaminated surface or groundwater in at least 14 states, while processing and enriching uranium for use in nuclear power plants requires water too. While natural gas power plants are usually much less water-intensive than coal or nuclear plants, the growing use of hydraulic fracturing, or “hydrofracking,” to extract natural gas has been linked with aquifer declines and water pollution. And storage of power plant wastes can lead to water quality problems; most coal ash, which is leftover after coal is burned, goes into landfills and surface impoundments, from which mercury, lead, cadmium, arsenic, and other toxics can leak out and contaminate water supplies.

Another important connection is the link between energy production, climate change, and water.  Today’s carbon emissions affect tomorrow’s water availability.  Heat-trapping emissions from human activity are driving up air and water temperatures, changing precipitation patterns, and increasing the risks of drought. And the power sector is a major source of heat-trapping emissions, accounting for one-third of the country’s total in 2009.

So what’s the solution? One of the easiest solutions is also the most cost-effective: recognizing the links between energy use and water helps people to recognize that using less electricity reduces both carbon emissions and demands on our water supply. Smart implementation of low- or no-water technologies, particularly renewable energy ones, means that we can substantially reduce the pressures that power plant cooling puts on our rivers and lakes.

Given the many connections between energy and water, the choices we make in the near future about how we produce and use energy will determine not only the extent to which we mitigate the worst impacts of climate change, but also how resilient our energy system is to the variability of our water resources and the many competing demands for it. Smart choices now will mean lower risks, greater energy security, and strong environmental and economic benefits.  

John Rogers, a senior analyst in the Climate and Energy Program at UCS, co-manages the organization's new Energy-Water Initiative, aimed at raising awareness of the energy-water connection, particularly in the context of climate change, and motivating and informing effective low-carbon and low-water energy solutions. Mr. Rogers formerly managed the Northeast Clean Energy Project, working primarily on renewable electricity standards and the Regional Greenhouse Gas Initiative. Mr. Rogers joined UCS in 2006 after working for 15 years on private and public clean energy initiatives, including as a co-founder of Soluz, Inc., a leading developer of clean energy solutions for rural markets. He earned a B.A. at Princeton University and a master's degree in Mechanical Engineering at the University of Michigan..