The researchers compiled data from the California Division of Oil, Gas and Geothermal Resources, which tracks oil and gas wells around the state. Researchers determined if water had been detected while drilling, and also gathered data about depth, salinity and pressure. After looking at 360 oil and gas fields spread across eight counties, the researchers say that they’ve documented a trove of fresh water just over half the size of Lake Michigan hidden in California’s bedrock 1,000 to nearly 10,000 feet below the surface. This is almost three times more groundwater than what was indicated in previous studies, many conducted...