Fracking is depleting water supplies in America's driest areas, report shows

Of the nearly 40,000 oil and gas wells drilled since 2011, three-quarters were located in areas where water is scarce, and 55% were in areas experiencing drought, the report by the Ceres investor network found.

Fracking those wells used 97bn gallons of water, raising new concerns about unforeseen costs of America's energy rush.

"Hydraulic fracturing is increasing competitive pressures for water in some of the country's most water-stressed and drought-ridden regions," said Mindy Lubber, president of the Ceres green investors' network.

Without new tougher regulations on water use, she warned industry could be on a "collision course" with other water users.

"It's a wake-up call," said Prof James Famiglietti, a hydrologist at the University of California, Irvine. "We understand as a country that we need more energy but it is time to have a conversation about what impacts there are, and do our best to try to minimise any damage."

It can take millions of gallons of fresh water to frack a single well, and much of the drilling is tightly concentrated in areas where water is in chronically short supply, or where there have been multi-year droughts.

Half of the 97bn gallons of water was used to frack wells in Texas, which has experienced severe drought for years – and where production is expected to double over the next five years.