The Water Replenishment District of Southern California (WRD) provides groundwater for 3.5 million residents in 43 cities of southern Los Angeles County. The District's service area, which covers the Central and West Coast Groundwater Basins, is about 420 square miles in extent. Prior to the formation of the District in 1959, over-pumping caused many water wells to go dry and sea water intrusion to contaminate coastal groundwater. WRD protects the basins through groundwater replenishment, deterrence of sea water intrusion, and monitoring and prevention of groundwater contamination.

WRD helps meet an average annual groundwater demand of 250,000 acre-feet in its service area. Long involved in the use of recycled water for groundwater replenishment, the District utilizes an average of 50,000 acre-feet of recycled water each year.