Thousands of feet beneath the surface of the state’s Central Valley, one of the world’s biggest agricultural hubs, there may be up to 2,700 cubic kilometers of usable groundwater — nearly three times more than the amount previously thought.

“It’s not often that you find a ‘water windfall,’ but we just did,” said study co-author Robert Jackson, a professor at Stanford. “There’s far more fresh water and usable water than we expected.”