America's oil and gas rush is depleting water supplies in the driest and most drought-prone areas of the country, from Texas to California, new research has found. 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. "[I]t 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. "Shale producers are having significant impacts at the county level, especially in smaller rural counties with limited water infrastructure capacity," the report said.