California's water supply to all sectors and uses splits into 30-41% groundwater (aquifers being 515 groundwater basins and subbasins) in non-drought years and up to 60% or more in drought years, 60-70% surface water (rainfall and snowmelt gathering in 10 major river basins, with Central Valley Watershed, the Sacramento-San Joaquin Delta, producing nearly half of the total), and a small percentage of desalinated sea water.

40% are used by agriculture (2.300.000ha irrigated area), 10% by all urban and municipal needs (including non-agricultural industries), 50% to replenish the natural habitats, environment, river deltas.

The annually used water has the quantity of 40 million acre-feet being 49 cubic kilometers, which are around 20% of the total of renewable water resources (own calculation), supplying water to a total population of 40 million.

According to the Water Education Foundation the average rainfall in California is 193 million acre-feet or 238 cubic kilometers, which is equivalent to the total of renewable water.

I am citing several sources, and figures do not seem to be always congruent. I have made use of the following organizations: California Department of Water Resources, Wikipedia, Water Education Foundation (Sacramento), California Department of Agriculture, California Water Watch, USGS Water Data for the Nation, Public Policy Institute of California (PPIC), US Department of the Interior, etc.

The California Department of Water Resources issues a new Water Plan every 5 years, the last update was in 2023.