Frequently asked questions
The Groundwater Replenishment System (GWRS) is the world’s largest water purification system for indirect potable reuse. It is operated by the Orange County Water District (OCWD) and located on its campus in Fountain Valley. It takes highly treated wastewater from the Orange County Sanitation District (OC San) that would have previously been discharged into the Pacific Ocean and purifies it using a three-step advanced treatment process consisting of microfiltration, reverse osmosis, and ultraviolet light with hydrogen peroxide. The process produces high-quality water that meets all state and federal drinking water standards. GWRS water is recharged into the local groundwater basin where it supports increased groundwater basin pumping by local cities and retail water districts.
After wastewater is treated at OC San, it flows to the GWRS where it undergoes a state-of-the-art purification process consisting of microfiltration, reverse osmosis, and ultraviolet light with hydrogen peroxide. The product water is near-distilled-quality.
- Pre-purification: Water used in the GWRS is first treated at OC San. OC San collects approximately 185 million gallons of wastewater per day and removes a high degree of impurities through several processes. A stringent source control program limits metals and chemicals flowing into OC San’s plants in Fountain Valley and Huntington Beach. The wastewater undergoes treatment through bar screens, grit chambers, trickling filters, activated sludge, clarifiers, and disinfection processes before it is sent to the GWRS.
- Microfiltration (MF): A separation process that uses polypropylene hollow fibers, similar to straws, with tiny holes in the sides that are 0.2 micron in diameter (1/300 the diameter of a human hair). By drawing water through the holes into the center of the fibers, suspended solids, protozoa, bacteria, and some viruses are filtered out of the water.
- Reverse Osmosis (RO): During the RO process, water is forced through the molecular structure of the membranes under high pressure, removing dissolved chemicals, viruses, and pharmaceuticals in the water. The end result is near-distilled-quality water so pure that minerals have to be added back in to stabilize the water.
- Ultraviolet (UV) Light: Water is exposed to high-intensity UV light with hydrogen peroxide to disinfect and to destroy any trace organic compounds that may have passed through the reverse osmosis membranes.
The GWRS is designed to have a production capacity of 130 million gallons of water per day (MGD) and a total production of 44 billion gallons per year. Approximately 30 MGD of GWRS water can be pumped into injection wells to create a seawater intrusion barrier. Another 100 MGD can be pumped to OCWD’s percolation basins in Anaheim where the GWRS water naturally filters through sand and gravel to the deep aquifers of the groundwater basin to increase the local drinking water supply. OCWD can also inject up to 10 MGD of GWRS water in injection wells located in the city of Santa Ana.
From the time it gets to GWRS from OC San, the advanced treatment process takes approximately 45 minutes. For GWRS water that is sent to recharge basins in Anaheim, it takes approximately six months to settle into the groundwater basin before it is pumped by local water retailers and served to customers.
The GWRS came online in January 2008, producing 70 MGD, enough for 600,000 people. It cost $481 million. It was expanded in May 2015, producing 100 MGD, enough for 850,000 people. The cost of the initial expansion was $142 million. The final expansion, completed in 2023, increases production capacity to 130 MGD, enough for one million people. It cost $284 million. Total project costs including all expansions are more than $900 million. Several grants and low-interest rate loans were received over the years by many state and federal agencies.
Construction cost: $481 million
- Annual Local Resources Program (LRP) operational subsidy of $121 per acre-foot over 23 years that amounted to $86.2 million. The LRP subsidy was provided and administered by the Metropolitan Water District of Southern California (MWD).
- $67 million grants from the 2000 California State Water Bond including $37 million from the State Water Resources Control Board (SWRCB) and $30 million from the Department of Water Resources (DWR)
- $5 million from the SWRCB through its Water Recycling Construction Program
- $700,000 from the California Energy Commission
- OCWD also received six Clean Water State Revolving Fund (CWSRF) loans in the amount of $162 million from the SWRCB
- $20 million from the U.S. Bureau of Reclamation (USBR) through its Title XVI program
- $500,000 from U.S. Environmental Protection Agency (EPA)
Construction cost: $142 million
- $137 million CWSRF loan from the SWRCB
- $1 million Proposition 84 Integrated Regional Water Management (IRWM) Implementation grant from the DWR
Construction cost: $284 million
- $3.6 million Proposition 1 IRWM Implementation grant from the DWR
- $5 million Proposition 13 and Proposition 1 grants from the SWRCB
- OCWD also received two CWSRF loans in the amount not to exceed $186 million from the SWRCB
- Low interest rate loan not to exceed $135 million from EPA’s Water Infrastructure Finance & Innovation Act (WIFIA)
Paving the way for the GWRS was Water Factory 21, an advanced wastewater reclamation plant and desalter that produced 15 MGD and operated from 1975 – 2004. It was here where OCWD first tested RO technology on municipal wastewater. Discussions about building the GWRS took place in 1997 when OCWD approached OC San about a joint project. Shortly after, a joint board committee was formed to discuss the preparation of required environmental impact studies, governance issues and public outreach. The Environmental Impact Report (EIR) was certified in 1999. In 2001, OCWD and OC San approved design and construction for the GWRS, and construction began in 2004.
The GWRS is the world’s largest facility of its kind and has garnered global attention for its innovative approach and use of technology to reuse a once wasted resource. It has emerged as one of the most celebrated civil engineering and water reuse projects in the world. It recycles 100% of OC San’s reclaimable flows, thereby maximizing water recycling efforts in the region.
Since inception, it has received more than 80 awards, welcomed 60,000 visitors, and set the Guinness World Record for most wastewater recycled to drinking water in 24 hours (by recycling 100 million gallons). OCWD and OC San were the first agencies in the Western Hemisphere to bottle advanced purified water under Assembly Bill 2022, which allows the bottling of advanced purified drinking water for educational outreach efforts.
The GWRS serves as a blueprint for other agencies around the world. The partnership between OCWD and OC San and public outreach were critical in achieving success and acceptance for this project. When other projects failed to get off the ground, GWRS was successful largely due to the early, proactive, and frequent outreach to the public and community stakeholders – outreach that continues today through an active speakers bureau program, facility tours, and presentations.