IN HOT WATERWater dis- charged from a coal or nuclear plant is hotter—by an average of 17°F in summer—than when it entered the plant.10 Roughly one- third of all U.S. power plants use once-through cooling11 and so return virtually all the water they withdraw. Still, these plants’ signicant water withdrawals can have a large impact on water quality, including tempera- ture. Half of all coal plants report releasing water in the summer at peak temperatures of 100°F or more.12 is thermal pollution can stress or kill sh and other wildlife. On Georgia’s Chattahoochee River, for example, several thousand sh perished each summer until Georgia Power retrot- ted its coal-red plants with cool- ing towers in 2002.13 Coastal power plants discharging warmed seawater can similarly harm local marine ecosystems.14 3
HIGH AND DRYWater troubles can shut down power plants. Just since 2004, water stress has led at least a dozen power plants to temporarily reduce their power output or shut down entirely, and prompted at least eight states to deny new plant proposals.15 During pro- longed heat in the summer of 2010, for example, water temperatures in the Tennessee River hit 90°F, forcing the Browns Ferry nuclear plant to signicantly cut the power output of all three of its reactors for nearly ve consecutive weeks—all while cities in the region were experiencing high power demands for air conditioning.16 4
Union of Concerned Scientists
drinking water 13%
U.S. freshwater withdrawals
Power plants account for the largest share of freshwater withdrawals in the United States.
5 WHAT DOES CLEAN MEAN? Clean energy can mean low carbon and low-water—or not. Increasing energy eciency will allow us to meet our energy needs with less electricity—and thus with less water use at power plants. Shifting to certain renewable energy technologies, such as wind turbines and solar photovoltaic modules, means generating electricity with essentially no water at all. But water usage by other renewable energy options varies widely. Technologies that can be particularly water-intensive include concentrating solar power (CSP), bioenergy, geothermal, and hydroelectric. Some CSP plants use far less water per unit of energy than a typical coal or nuclear plant to cool steam; other CSP facilities use more.17
Nuclear Regulatory Commission
Understanding Power Plant Water Use
Water withdrawal: The total amount of water taken from a surface- or ground-water source. In most cases, some fraction of that water will be returned to the water source and available for other withdrawals.18 Water withdrawal can become a large problem during drought and heat waves: water can be too warm, or levels too low, to cool the power plant, or the cooling water used by the plant can be made too warm to safely discharge.
Water consumption: That part of with- drawn water that is not readily available for re-use because it is evaporated in power plants. The amount of water consumed by power plants is a particular concern in water-constrained regions (including large parts of the western United States).
6 MPG OR GPM?Powering your car with ethanol may use dozens of gallons of water per mile. e “water footprint” of conventional biofuels, such as corn ethanol, can be very large. Creating a single gallon of ethanol consumes, on average, about 100 gallons of freshwa- ter. In some regions, however, ethanol production can take three or more times that amount—mostly depending on water needs for irrigation.19 Water requirements for some other forms of biofuel are lower. Estimates indicate that it will require only 2 to 10 gal- lons of water to produce each gallon of “cellulosic” biofuel from drought- resistant grasses and waste wood.20
In 2007 and 2010, the Browns Ferry nuclear plant (Athens, AL) was forced to curtail power production of all three of its reactors. During these events, electricity needs were met by other power generators— though at higher prices. Such events illustrate the risks and costs that are “hard-wired” into today’s electric- ity system: a lack of adequate water, or adequately cool water, can crip- ple power plants precisely when we most need electricity.