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Dig Deep Enough and You’ll Find a Lot of Fresh Water Under California’s Central Valley

The water is there, scientists report, but keeping it safe and sustainable is another matter.

By Nathan Collins


A view of a fallow field in Tulare, California. (Photo: Justin Sullivan/Getty Images)

Though California’s water emergency is technically over, the state is likely to feel the effects of the drought for years to come. This has many wondering how to discover new water sources in the parched state. Now, researchers report they’ve found vast reserves of water deep underground—but whether we can get it to the surface safely and in a sustainable fashion remains unclear.

“Our findings indicate that California’s Central Valley alone has close to three times the volume of fresh groundwater and four times the volume of USDWs [underground sources of drinking water] than previous estimates suggest,” Stanford University researchers Mary Kang and Robert Jackson write in Proceedings of the National Academy of Sciences. “Therefore, efforts to monitor and protect deeper, saline groundwater resources are needed in California and beyond.”

Although researchers know there’s water deep underground, they don’t have a very good idea of exactly how much water there is, or whether it’s safe to drink. The most current estimate of the size of the Central Valley Aquifer—roughly a thousand cubic kilometers—is 20 years old.

There were around 2,700 cubic kilometers of drinkable water.

To get a better sense of that situation, Kang and Jackson looked to data from the California Department of Conservation’s Division of Oil, Gas, and Geothermal Resources, which collects data on underground oil and gas pools along with wells drilled into the ground, often to great depths.

That data revealed a surprising amount of drinkable water. The cleanest and most abundant underground water was found in Kern County, north of Los Angeles, but Yolo and Fresno counties also had sizable sources of drinkable water stored at depths up to 3,000 meters. Overall, there were around 2,700 cubic kilometers of drinkable water, much more than previous estimate of around 1,020 cubic kilometers, according to Kang and Jackson.

But drawing on those underground water sources comes with a number of risks. For one thing, most of them of them are near oil and gas wells, meaning they’re vulnerable to contamination. It’s also possible that draining deep wells could worsen the Central Valley’s already serious ground subsidence problem. More studies will be needed, Kang and Jackson conclude, before California can actually rely on underground sources for its water.