California groundwater pumping by region

The Business Journal
Study: Valley uses highest share of groundwater
According to the study by the Public Policy Institute of California, groundwater typically accounts for about 35 percent of the water used by California's farms and cities, 29 percent during the wettest years and 44 percent in the driest years.
That's an average of about 15.2 million acre-feet a year compared to California's overall agriculture and urban water use of 42 million acre-feet.
In the Central Valley, the share is even higher. Farms and cities in the San Joaquin River basin, for example, pump 26 percent of their groundwater in wet years and 45 percent in dry years for an average of 2.78 million acre-feet per year. That's 18 percent of the state's total share of groundwater use.
The Sacramento River basin has the same share, pumping 26 percent of its water from the ground in wet years and 31 percent in dry years for an average of 2.67 million acre-feet per year.
The Tulare Lake basin, which accounts for 38 percent of the state's groundwater use, sees 23 percent of its water pumped up from the ground during wet years and 71 percent in dry years for an average of 5.7 million acre-feet per year.
Farms and cities in the Central Coast are even more reliant on groundwater, pumping 81 percent of their water in wet years and 89 percent in dry years. However, at an average of 1.1 million acre-feet per year, that's only 7 percent of the statewide share of groundwater.
The San Francisco Bay region has the lowest groundwater use in the state at an average of 145,000 acre-feet pumped every year, just 1 percent of the statewide share.
The South Coast accounts for 10 percent of the state's groundwater share at an average of 1.58 million acre-feet pumped per year, while the North Coast makes up a 2 percent share at an average of 363,000 acre-feet per year.
Groundwater use is largely unregulated under California law, leading to excessive pumping, or overdraft.
According to the study, this results in higher energy costs due to deeper wells, infrastructure damage from sinking lands and nitrate contamination that can pollute local drinking water supplies.
The study stated that the state would benefit from better groundwater management like limiting pumping in normal and wet years, increasing groundwater storage by spreading it on fields to percolate through the soil or injecting water into wells and charging fees to fund recharge programs.