There’s a vast amount of untapped water in California, but whether it can make any difference for the drought-stricken state remains unclear. A new Stanford study indicates California’s groundwater supply is three times greater than previous estimates and could represent a potential “water windfall,” its authors say.

“There’s far more fresh water and usable water than we expected,” said Robert Jackson, co-author of the study, published Monday in the Proceedings of the National Academy of Sciences.