The Coachella Valley averages about 3 inches of rain a year, yet about 95 percent of the drinking water Desert Water Agency serves to the community and is pumped from wells, according to the agency. Nearly all the water used in the valley comes from a groundwater basin, or aquifer, beneath the surface, Desert Water Agency says. A local water-conservation campaign describes it as a body of permeable rock that stores water, 500 to 1,300 feet below the valley floor, holding about 39 million acre-feet, or roughly 13 trillion gallons. Desert Water Agency, which serves Palm Springs, operates 27 wells drilled 1,000 to 1,200 feet deep, with pumps set as far down as 500 feet. The agency says the water is of high enough quality that it only needs chlorination, as state regulations require, before delivery.