How water works in Orange County

Orange County receives its water from multiple sources. The Orange County Groundwater Basin provides 77% of the drinking water supply to 2.5 million people in north and central Orange County. South Orange County receives imported water from the Colorado River and northern California via the State Water Project. 

North and central O.C.

The Orange County Water District (OCWD), servicing 2.5 million residents in north and central Orange County, manages the Orange County Groundwater Basin (Basin) and refills it with many different water supplies: water from the Santa Ana River, which includes rainfall, snowmelt and treated wastewater from upstream water users, local rainfall, imported water from the Colorado River and northern California, and purified wastewater from the Groundwater Replenishment System (GWRS). 

The GWRS, the world's largest water purification system for indirect potable reuse, currently produces 100 million gallons of high-quality water that exceeds drinking water standards and serves as a locally-controlled, drought-proof water supply. In early 2023, the GWRS will complete its Final Expansion that will produce 130 million gallons of water a day, enough to serve 1 million people daily. OCWD is also implementing a regional groundwater banking program to ensure long-term reliability and increasing stormwater capture behind Prado Dam, where water eventually gets recharged into the Basin and becomes a part of the drinking water supply.

Thanks to OCWD’s innovative water management programs, 19 cities and retail water agencies can pump about 77% of their water demands from the Basin. They get the remaining 23% from imported supplies brought in by the Metropolitan Water District of Southern California (MWD) and served through its local subsidiary member agency, the Municipal Water District of Orange County (MWDOC).  

South O.C.

Eight retail water agencies deliver drinking water to the remaining 600,000 residents and businesses located in south Orange County. These communities do not reside within the boundaries of the Basin and are heavily dependent on imported water for their drinking water supply. As such, most of their drinking water supply is imported from hundreds of miles away via MWDOC.

Cost of water in O.C.

The cost of groundwater is $507/acre-foot, about half the cost of imported water, which is $1,143/acre-foot. Retail water agencies in Orange County establish the price of water delivered to customers. The rate charged for water is impacted by multiple factors, including the cost of groundwater, the cost of imported water, the cost to construct, operate and maintain pipelines, reservoirs and pumps to deliver water to homes or businesses, and the administrative cost of operating a retail water system. Retailers' rates can vary depending upon the age of the water system, how much groundwater is used versus more expensive imported water, and other factors. For this reason, OCWD attempts to maximize the amount of groundwater available to retail agencies, while sustainably managing the basin.

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