About 30 percent of California’s total annual water supply comes
from groundwater in normal years, and up to 60 percent in drought
years. Local communities’ usage may be different; many areas rely
exclusively on groundwater while others use only surface water
supplies. Contrary to popular opinion, groundwater does not exist
in underground lakes. Groundwater fills pores (spaces) between
sand, gravel, silt and clay in water-bearing formations known as
Many cities rely on local water projects for all or a portion of
their supplies. These projects typically were built and are
operated by local public water districts, county water
departments, city water departments or other special districts.
Nearly 600 special purpose local agencies in California provide
water to their areas through local development projects and
imported supplies. A number of local agencies may also operate
flood control and wastewater treatment facilities in addition to
providing drinking water.