U.S. water use down but migration to West a concern

Water shortages are seen as one of the biggest threats to the planet as the global population grows and climate change makes dry areas drier and inundates already wet areas with more frequent storms that play havoc with water quality.

Total U.S. water use declined in the five years to 2005 as a growing population has become more efficient. But climate change will exacerbate water shortages in hot areas and further threatens water sufficiency, said Peter Gleick, president of the Pacific Institute, which produced the study based on U.S. Geological Survey data.

A switch to sprinklers in agriculture, better industrial efficiency and more water-wise homes have cut America's total water use slightly in recent years and kept it roughly flat since 1975, despite an 81 million increase in the country's population.

"We've broken the link between population and the economy and water use. In particular, we've broken that link by dramatically improving our water use efficiency," Gleick said.

"The bad news hidden in these numbers is that our population is growing in the hottest, driest, most water scarce regions of the country."

Water use by thermal power plants -- those fueled by coal, nuclear and natural gas -- which need coolants to improve efficiency of running a turbine, has been rising slowly since 1985 and accounted for just under half of all water withdrawals in 2005, said Gleick.

"We need to produce more energy, not with fossil fuels, which consume a lot of water, but with renewables that don't," he said.

(For more environmental news see our Environment blog at http://blogs.reuters.com/environment)

(Reporting by Peter Henderson; editing by Chris Wilson)