Efforts to wean America's automobiles off gasoline are running into the law of unintended consequences. Methanol wears out engine components, and corn-based ethanol has squeezed corn supplies. Even bypassing liquid fuel altogether may be problematic: New research suggests that flooding the roads with plug-in vehicles could cause a significant, though potentially manageable, drain on regional water sources.
Present-day hybrid vehicles employ a small electric motor--in addition to an internal-combustion engine--to improve fuel efficiency. Plug-ins represent the next step in green car evolution. Still in development, they will use advances in battery technology to allow car owners literally to plug into the electric power grid and recharge overnight.
A hypothetical plug-in vehicle would require up to 30 kilowatt/hours of electricity to recharge for a typical day's driving. It may not sound like much, but multiplied by millions of plug-in cars on the road within the next decade, the drain on water resources would add up. That's because electricity comes from very large--steam--turbine generators and nuclear reactors, which must be cooled with water pumped in from streams and rivers. Most of that water eventually is returned from whence it came, though a small amount--less than 4%--is lost to evaporation. "People generally don't connect increased demands on water resources with a large fleet of electric-powered vehicles," says mechanical engineer Carey King of the University of Texas (UT), Austin.
To gauge the impact of this increased demand for water, King and UT colleague Michael Webber reviewed existing literature on the power needs and affiliated water consumption of electric versus gasoline vehicles. Their report, to be published in the June issue of Environmental Science & Technology, suggests that supporting a large fleet of plug-ins--say, 10 million by the year 2015--would require an additional 1.1% or so of water used by electric power plants. Ratcheting up to 50 million vehicles--a possibility as early as 2020, King says--would require up to 3% more water. That could be a problem in the American West, which is undergoing drought and where automobile use is high, notes Webber. But given the time frame, he adds, there is room to plan and adjust, such as by studying water-conserving alternatives.
Environmental scientist Dalia Patino-Echeverri of Duke University in Durham, North Carolina, says the study presents "a good way to start thinking about this problem," and she urges more work on the issue's potential impact in water-scarce regions. "Capital investments in the electricity industry until now have been driven by considerations about fuel prices and air-quality issues," she says, adding that perhaps too little attention has been paid to water demands.