Orange County Water District

A collaborative effort between the Orange County Water District (OCWD) and the Orange County Sanitation District (OCSD), the Groundwater Replenishment System (GWRS) is the world’s largest advanced water purification system for potable reuse. OCWD receives OCSD’s stringently controlled, secondary-treated wastewater that otherwise would be sent to the Pacific Ocean and purifies it using a three-step process. Consisting of microfiltration, reverse osmosis and ultraviolet light with hydrogen peroxide, the GWRS purification process produces high-quality water that exceeds all state of California and federal drinking water standards. More than half of the GWRS water is injected into recharge basins where it naturally percolates into the groundwater basin and supplements drinking water supplies. Thirty-five million gallons each day are also injected into a series of seawater intrusion barriers that protect the basin from saltwater contamination.

Operational since January 2008, and since an expansion in 2015, the GWRS can produce 100 million gallons (MGD) (378,000 cubic meters) of water every day. This is enough water to meet the needs of about 850,000 residents in north and central Orange County. Ultimate capacity for the GWRS is projected at 130 MGD (492,000 cubic meters). GWRS water contributes about 25 percent of the basin freshwater supply.

This purified water decreases dependence on costly imported water from Northern California and the Colorado River, uses one-third the energy required to desalinate seawater, helps to make the region drought-resilient, protects the groundwater basin from saltwater contamination, and protects the environment by reusing a precious resource.

OCWD and OCSD are tapping into every possible drop of water, setting an example for other agencies around the globe.

For additional information about OCWD and OCSD, please visit and, respectively.