California water districts expand world’s largest potable reuse system

The world’s largest advanced water purification system for potable reuse just got even bigger, as a joint project of the Orange County Water District (OCWD) and the Orange County Sanitation District (OC San) completed an expansion earlier this year that can provide enough water for a million people. 

The expansion project for the Groundwater Replenishment System (GWRS) increased treatment capacity from 100 to 130 million gallons per day (MGD). The facility now recycles 100% of local reclaimable wastewater flows, maximizing water recycling efforts in the region. (Pictured right, an aerial view of the system expansion site.)

The GWRS’s advanced water purification facility (AWPF) takes secondary treated wastewater from OC San and treats it to drinking water standards through microfiltration, reverse osmosis, ultraviolet light, decarbonation, and lime addition. The product water is sent to injection wells and recharge basins that replenish the groundwater basin with new water. Cities in north and central Orange County pump this water out through production wells to deliver to residents in their cities as tap water.

“The success of this project stems from the original vision from board members from both agencies (OCWD and OC San), OCWD staff involvement, reporting from engineering/process consultants, and advisory groups that studied and validated the science and engineering concepts,” said Sandy Scott-Roberts, GWRS program manager. “Additionally, the investment in public outreach at the very early planning phase was crucial to educate the public and community about GWRS and to show them that implementing a project like this is safe, will help Orange County reduce reliance on imported water, and help keep water rates low.”

The $284 million expansion project was funded through a variety of sources, including a low interest loan of $135 million from the U.S. Environmental Protection Agency’s Water Infrastructure Finance & Innovation Act (WIFIA), a program that AWWA helped craft and champion through the legislation process.

Because two-thirds of California’s population lives in the southern part of the state where less than one-third of the state’s precipitation falls, it’s important for water agencies to work together to solve long-term water supply challenges and decrease dependency on imported water, Scott-Roberts explained.

OCWD and OC San have worked together for more than 40 years to provide a reliable, environmentally sustainable supply of safe, clean water with the GWRS project.

“Projects like GWRS, with two completely separate agencies involved, really benefit from the collaboration and support from the board of directors and upper management staff from the two agencies,” said Scott-Roberts. “For this project, OCWD and OC San created a joint steering committee on which board members from both agencies participated. This board level support would be encouraged to the staff level and helped ensure all were working together to get the project completed.”