The Groundwater Replenishment System (GWRS) has reached a major production milestone of half a trillion gallons of purified water as it marks 18 years of service this month. A joint project of the Orange County Water District (OCWD) and the Orange County Sanitation District (OC San), the GWRS is the world’s largest advanced water purification system for indirect potable reuse, reducing dependence on imported supplies and strengthening water reliability for Orange County. 

“OCWD and OC San invested early in critical water reuse and recharge infrastructure, and Orange County has reaped the benefits for 18 years,” said OCWD President Denis R. Bilodeau, P.E. “Surpassing half a trillion gallons is an achievement that underscores the role of the GWRS in turning a once-wasted resource into a reliable, locally controlled drinking water supply for the communities we serve.”  

The GWRS purifies highly treated wastewater using a three-step treatment process of microfiltration, reverse osmosis and ultraviolet light with hydrogen peroxide. The result is high-quality water that is pumped to recharge basins in Anaheim, where it naturally percolates into the Orange County Groundwater Basin, managed by OCWD, and becomes part of the drinking water supply for 2.5 million people in north and central Orange County. GWRS water is also pumped into injection wells located along the Orange County coastline to create a seawater intrusion barrier that protects groundwater supplies. 

Operational since 2008, the GWRS completed its initial expansion in 2015, increasing production from 70 million gallons per day (MGD) to 100 MGD. With its final expansion in 2023, the system now recycles 100% of OC San’s reclaimable wastewater flows and produces up to 130 MGD — enough to serve 1 million people.  

“Reaching half a trillion gallons is a powerful reminder of what long-term vision and operational excellence can achieve,” said OC San Board Chairman Ryan Gallagher. “By investing in advanced treatment and infrastructure, OC San ensures every drop of reclaimable water is put to its highest and best use. This milestone reflects our commitment to protecting public health, strengthening water resilience, and delivering sustainable solutions for Orange County today and for generations to come.”

Over the years, GWRS water has become a primary source for replenishing the groundwater basin and has enabledOCWD’s 19 cities and local water retailers to pump more water from the basin. The GWRS also reduces the need to purchase costly imported water from Northern California and the Colorado River, contributing to a more cost-effective, drought-resilient water supply for the region. 

As part of OCWD and OC San’s public education efforts to build understanding and acceptance of potable reuse, the agencies have distributed thousands of bottles of GWRS water. California Assembly Bill 2022 allows advanced purified water to be bottled and distributed at no cost for educational purposes, and OCWD and OC San were the first in the Western Hemisphere to do so. The agencies will introduce newly labeled GWRS bottled water at tours and other outreach events to support their continued commitment to water education. 

For more information, OCWD invites the public to book a facility tour, watch an on-demand general or technical tour video, or visit the GWRS website.