Running vehicles on alternatives to fossil fuels could stress scarce water resources, US scientists have warned.
Michael Webber and Carey King, from the University of Texas at Austin, suggest that powering America's cars with electricity, rather than gasoline (petrol), could triple the nation's water consumption. And biofuels, derived from crops requiring irrigation, are even more water-intensive, according to a further unpublished analysis by the team.
'This doesn't mean that we shouldn't try to switch to alternative fuels - but if we're going to do it, we need to be aware of a potential downside,' Webber explains.
Water is the main coolant in the coal, gas, or nuclear power plants that largely supply vehicles with electricity. Webber and Carey calculate that when switching from 'gasoline miles' to 'electric miles', approximately three times more water is evaporated into the atmosphere, and seventeen times more water withdrawn for cycling around the plant before being returned to a river or lake.
While parts of the US are water-rich, limited water availability in some drought-stricken areas (such as the south-east) might hinder the growth of power plant systems that would be needed to cope with the greater demand by electric vehicles, says Webber.
He recommends switching to less water-intensive methods of generating energy: for example, solar or wind power; using non-irrigated biofuels; or using reclaimed or salt water to cool power plants.
Peter Gleick, president of the environmental think-tank the Pacific Institute in Oakland, California, thinks that the added water demands Webber identifies may not be very significant. 'In regions where water is scarce, the key will be to produce fuels, or electricity, where water is less of a constraint,' he said.
But both Webber and Gleick feel that the link between water and energy has been neglected amid understandable concerns about security and carbon-costs of energy supplies. 'We've typically considered water and energy separately, and it is no longer appropriate to do so. We can no longer push for energy policies that ignore our water challenges, just as we can't push for water policies that ignore energy costs and benefits,' Gleick said.
Richard Van Noorden