Plugging in to more water use
A big shift to electric vehicles could strain water resources in dry places.
A fully electric car never fills up at the gas pump, but it does use water. No, the water doesn't fuel the car, but power plants use quite a bit of water to make the electricity that surges through the plug. And as more electric vehicles hit the road, power plants will use more water. Driving a car on electricity consumes three times more water than driving with gasoline, mile for mile, according to new research published in ES&T (DOI: 10.1021/es0716195).
Water use is not an issue that people typically associate with plug-in vehicles, which have many environmental benefits, say study coauthors Carey King and Michael Webber of the University of Texas Austin (UT). However, "adding any additional strain on water can be a problem in some places," says Webber, who is associate director of the Center for International Energy and Environmental Policy at UT. "If you're in the water-rich Northeast, it's no problem, but if you're in the water-strained Southwest, like Southern California, it might be a problem."
Any power plant that runs steam turbines uses water, whether fired by coal, natural gas, or nuclear energy, says King, a mechanical engineer at the Bureau of Economic Geology at UT. Many plants consume water by running it through cooling towers where it evaporates away. Plants can also tie up water resources via withdrawal, in which plants recycle water that is drawn from a reservoir. Powering a plug-in electric vehicle withdraws 17 times more water per mile than fueling a gasoline vehicle, the authors say.
All told, electricity generation in the U.S. consumes more water than any other activity except irrigation, accounting for about 195 billion gallons (Bgal) per day, or nearly half of all withdrawal, according to the U.S. Geological Survey. Refining gasoline uses some water too; the new study used this for comparison.
According to King and Webber's analysis, replacing 25% of U.S. cars, light trucks, and SUVs with electric vehicles would consume roughly an additional 100 Bgal per year of water. "It's quite a lot," says Peter Gleick, a water expert and president of the Pacific Institute, an independent think tank in California. (He's also the "very proud owner" of a hybrid Toyota Prius, he says, which does not plug into the grid but uses electricity generated from braking power.)
Gleick says the total amount of extra annual water consumption calculated in the paper translates to about 300,000 acre-feet per year. "For comparison," he notes, "the entire urban sector of California—all the residential, commercial, and industrial use—uses about 800,000 acre-feet." The impact of the extra water use will depend on how it is spread across the country, Gleick says.
In California, state programs and utilities are working to bump up the number of plug-in hybrid electric vehicles (PHEVs), which would reduce air pollution and greenhouse-gas emissions. But the state is also water-stressed and its water consumption for generating electricity could grow more than 60% from 2000 to 2020, according to the Electric Power Research Institute. For example, "if Southern California Edison is going to be running a lot more power at night for plug-in hybrids, they're going to need more cooling water," Webber says. He notes that generating the electricity should not be a major problem for utilities. This squares with a recent study in ES&T, which found that "the U.S. currently has sufficient spare nighttime electricity capacity to charge a large fleet of PHEVs," enough to easily accommodate a light-duty fleet of one-third PHEVs.
"We're not trying to put a black eye on plug-ins," Webber says. "They're very appealing for a lot of reasons." They take advantage of off-peak power capacity, he notes, and they replace oil. Gleick agrees, adding that water use "is only one of the trade-offs, the most important being the emission of greenhouse gases and dependence on foreign oil."
In the future, utilities will face rising electricity demand for many uses, says Tom Kleckner, a spokesperson for the Texas utility Luminant. He says planning for water will be especially important in developing new power plants and notes that efficient technology and greater use of renewable energy sources can help reduce water needs. "Water is not an issue with wind," he says, because wind has the benefit of being produced mainly at night, when plug-in owners could be recharging.
