As the state faces a growing threat from drought, an increasing number of water agencies are planning to require flow meters on agricultural wells, part of a landmark effort to measure and constrain pumping that used to be free and unlimited. It's a controversial step aimed at protecting water supplies that could change cultivation practices in the Golden State's thirsty fields.

"It's hard to be as efficient as possible if you don't know how much water you're using," said Sierra Ryan, interim water resources manager for Santa Cruz County.

Under the state's tough new groundwater protection law, "we now have a legal obligation to manage our groundwater sustainably," she said. "And we cannot manage the basin with such large uncertainties in our water use."