The porous soil below the gravel and sand here, which are carried here from the Sierra Nevada by the Kern River, is ideal for the purpose. “It’s a huge bucket,” said Florn Core, the former water resources manager for the City of Bakersfield, which is located in a natural desert where rainfall averages 5.7 inches annually.

Yet with its local supplies and water deliveries from the state and federal governments, Kern County is an agricultural paradise of carrots, citrus, pomegranates and pistachios.

Changes in the agricultural economy over the last 15 years, including the rising popularity of pomegranates and pistachios, prompted many farmers to switch to permanent crops, taking away the option of letting fields lie fallow in dry years. So water banking expanded.

Since 1978, when water banking started here, 5.7 million acre-feet — about a third of the annual flow of the Colorado River — has been stored in the two largest banks, said James M. Beck, the general manager of the Kern County Water Agency, which regulates local use. The two banks’ combined storage capacity is about 2 million acre feet.

Pumping out huge amounts of stored water in dry years was thought to have little impact on the underground geology — at least until Mr. Key’s shower head sputtered. Now engineers believe it reversed the area’s underground hydraulic gradient, turning a hill-shaped water table, accessible by shallow wells, into a valley. The trigger for the huge withdrawals was a drought that began in 2007. Kern County’s allocation of water from Northern California was cut. Then, in the 40 months beginning in March 2007, roughly half the banks’ capacity was pumped out to keep fruit and nut trees alive.

“I don’t think anyone fully appreciated the magnitude of the impact they would have,” said Mr. Averett of the Rosedale-Rio Bravo Water Storage District.

POM Wonderful, part of the fruit-drink empire owned by Stewart and Lynda Resnick, makes its profits from pomegranate trees kept green by the Kern Water Bank Authority. The authority, technically a public agency, is controlled by the Paramount Farming Company, which like POM, is a subsidiary of Roll Global, a company owned by the billionaire Resnicks.