While plug-in hybrids offer great increases in fuel efficiency, they may come at a surprising cost: water. A recent study from Environmental Science & Technology found that plug-ins require the consumption of 3 times more water, and the withdrawal of 17 times more water, than their gasoline counterparts. As Popular Mechanics pointed out last week:
A 30-mile commute in a gasoline-powered car would require the withdrawal of 18.9 gallons of water… The same commute in a plug-in hybrid electric vehicle (PHEV), meanwhile, would take a whopping 318 gallons…
So what accounts for the increase in water usage? PHEV’s don’t require water directly, but the power plants that power them do:
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.
This is enough of an increase to warrant consideration by public policy-makers, especially in arid climates. If 25% of the nation’s fleet converted to plug-in vehicles it would require an additional 1 billion gallons of water for electricity generation. For comparison, that’s almost half the total urban water used by the state of California in one year.
But no one, including the study authors, is saying that plug-in hybrids should be blacklisted. It just adds an important consideration for water-stressed areas that have plans for a grid-based automotive fleet. It also highlights the importance of using sustainable (wind, solar) sources of electricity for electric vehicles.
And as far as the alternatives go: PM pointed out that growing a bushel of corn requires 2200 gallons of water, which only makes 2.7 gallons of ethanol. I would take a fleet of plug-ins over a fleet of Flex-Fuel vehicles any day.
See the study here.
ES&T (Feb. 20, 08): Plugging in to more water use
Popular Mechanics (Mar. 7, 08): Plug-in Cars Could Drain U.S. Water Supply, Researcher Says