California’s underground aquifers can hold vastly more water than its reservoirs — between 850 million and 1.3 billion acre-feet of capacity below ground, compared to about 38.1 million acre feet above ground, according to the Department of Water Resources. 

Local districts have been carefully tending groundwater for decades. The Orange County Water District, for instance, pumps highly treated water underground to keep seawater at bay and replenish local drinking water stores. In the Southern San Joaquin Valley, water suppliers funnel surface water into underground storage at the controversial Kern Water Bank, largely for agricultural irrigation.

The Newsom administration has called for increasing groundwater recharge yearly by at least 500,000 acre-feet. But ongoing challenges remain to widespread groundwater recharge. 

“There’s a lot more empty aquifers than there are unclaimed sources of water in California,” said Michael Kiparsky, Water Program Director at the Center for Law, Energy & the Environment at UC Berkeley School of Law.

It’s not just about the amount of water, Kiparsky said, it’s also about the logistics. California will need to ensure there’s enough capacity to quickly move flood flows to the right basins for recharge during California’s brief rainy season. 

Unless that bottleneck is widened, plans to end the overdraft of depleted aquifers in the San Joaquin Valley are calling for more groundwater recharge than is likely realistic, according to the Public Policy Institute of California.