Frequently asked questions

The Groundwater Replenishment System (GWRS) is the world's largest advanced water purification system for potable reuse. The GWRS takes highly treated wastewater that would have normally 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 GWRS produces up to 100 million gallons (379,000 cubic meters) per day of high-quality water that exceeds all state and federal drinking water standards for nearly 850,000 residents in north and central Orange County.

In the mid-1990s, the Orange County Sanitation District (OC San) faced the possibility of having to build a second ocean outfall that would have cost approximately $200 million.  At the same time, the Orange County Water District (OCWD) was faced with continued problems of seawater intrusion and the need to expand its Water Factory 21 (WF 21) from 22.6 million gallons (85,600 cubic meters) per day to 35 million gallons (132,500 cubic meters) per day. 

At the time, California had just experienced a severe drought. Water experts also projected droughts would occur three out of every 10 years, that there would be increases in demand due to population growth, and that the demand and cost of imported supplies would increase in the near future.  Faced with these future challenges, OCWD built upon its long-history of successfully treating wastewater at WF 21 for its seawater barrier and decided to implement advanced processes to purify the wastewater and send it to recharge basins, where it would ultimately become part of north and central Orange County’s drinking water supply.

The GWRS can produce up to 100 million gallons (379,000 cubic meters) of water per day of near-distilled, high-quality water.  That is enough to meet the needs of nearly 850,000 residents in north and central Orange County. After its final expansion is complete, production will increase to up to 130 million gallons of water per day.

After more than ten years of planning and construction, the GWRS came on-line in January 2008. By October 2010, it had already produced more than 50 billion gallons (189 million cubic meters) of new, high-quality water.

The capital cost to build the GWRS was $481 million (U.S. Dollars) and was funded through $92.8 million in local, state and federal grants. Funding included $37 million from the State Water Bond (Proposition 13) approved by California voters in 2000, $30 million from the California Department of Water Resources, $5 million from the State Water Resources Control Board awarded in 2002, $20 million from the United States Bureau of Reclamation’s Title XVI program, $300,000 from the California Energy Commission, and $500,000 from the Environmental Protection Agency. OCWD and OCSD cost shared the remaining $388 million.

The GWRS initial expansion, completed in 2015, cost $142 million.

It costs approximately $40 million a year to operate the GWRS. Roughly $15 million is for power alone; however, it is important to note that the GWRS water can be produced using half the energy required to pump imported water from Northern California to Orange County.  Other maintenance costs include $6 million for chemicals, $7 million for membrane and ultraviolet lamp replacement and $10 million for operating and management (O&M) staffing.  The Metropolitan Water District of Southern California (Met; MWD), the importer of water for all of Southern California, subsidizes $7.5 million annually (for 12 years) to help operate the facility because it creates significant amounts of new water and helps to alleviate demand from fragile and unreliable imported water supplies that MWD is responsible for delivering to Southern California.

Without any grants factored in, the cost to produce GWRS water is $850 per acre-foot (AF). With grants and OC San’s contribution factored in, the cost to produce GWRS water is $525 AF. Even without subsidies, the cost of GWRS water is comparable to the cost of imported water. By 2011, the cost of imported supplies became greater than GWRS water. GWRS water is also drought-proof and more reliable than imported supplies.

The GWRS uses less than half the energy required to transport water from Northern California to Southern California. The energy savings is enough to power more than 21,000 homes each year.

Purifying wastewater is about one-third the cost of ocean desalination because there are far fewer dissolved solids (salts) to remove from wastewater – 1,000 mg/L as compared to 35,000 mg/L in ocean water. Removing that high concentration of salts requires three times more energy, additional membranes, and a shorter RO membrane life-span.

About 20 acres (81,000 square meters).

Yes, the Public Utilities Board of Singapore operates five NEWater factories, producing 50 million US gallons (190,000) per day. Some of the NEWater is used at micro-chip fabrication plants and for other non-potable industrial applications. The rest is fed into nearby reservoirs. NEWater is currently able to meet 30% of Singapore's water requirements. Additional facilities include West Basin Municipal Water District Edward C. Little Facility in El Segundo, Water Replenishment District Leo J. Vander Lans facility in Long Beach and Scottsdale Water Campus in Scottsdale, Arizona. For more information about water reclamation and the different processes and uses, visit the WateReuse Association website at www.athirstyplanet.com.

It is a 10,000 gallon (38 cubic meters) tank.

Yes, the highly-treated wastewater is filtered through a strainer and sodium hypochlorite (bleach) is added to prevent biofouling on the microfiltration membranes.

The main types of pumps are horizontal centrifugal and vertical turbine pumps.  Most all pumps in the GWRS have a variable frequency drive (VFD) to save energy.

Up to 130 million gallons (492,100 cubic meters) of treated secondary effluent is delivered to MF at the GWRS through a 96 inch (2.4 meters) diameter pipe.

Each MF membrane module costs approximately $720. There are a total of nearly 25,000 MF modules. They have a lifespan of five to seven years. Each RO membrane module costs approximately $450. There are nearly 22,000 RO membrane modules in the GWRS.  Each has a lifespan of approximately five years.

MF membranes are made of polypropylene hollow fibers, similar to straws, with tiny holes in the sides that are .2 micron in diameter (1/300 the diameter of a human hair).

RO membranes are made of polyamide (a polypropylene structure with a thin separating polymerizing layer on top).

The process of osmosis through semi-permeable membranes was first observed in 1748 by Jean Antoine Nollet, a French clergyman and physicist. For the following 200 years, osmosis was only a phenomenon observed in the laboratory. In 1949, the University of California at Los Angeles (UCLA) first investigated desalination of seawater using semi-permeable membranes. Researchers from both UCLA and the University of Florida successfully produced fresh water from seawater in the mid-1950s, but the flux was too low to be commercially viable.

The first commercial RO membrane was created by scientists at UCLA in 1959. Inspired by President John F. Kennedy’s administration goal “to go to the moon and make the desert bloom”, RO research increased in the 1960s. OCWD was the first agency in the world to use RO on wastewater in the mid-1970s.  Since then, RO technology has been used throughout the world to clean wastewater and groundwater and desalt ocean water.

Kraemer, La Palma, Miller, and Miraloma basins located in Anaheim.

The 13-mile (21 kilometers) pipe to Anaheim is a cement, mortar-lined and coated steel reinforced pipe that ranges in diameter from 60 to 78 inches (1.5 -2.0 meter).

2,250 Horse Power (HP) (1.7 million watts) motors power the pumps that move the water to Anaheim and 600 HP (441,000 watts) motors power the pumps that move the GWRS water to OCWD’s seawater barrier.

About 30 percent of the water that refills the basin comes from the GWRS. The rest of OCWD’s water is from the Santa Ana River, rainfall and imported water from Northern California and the Colorado River.

Absolutely.  The GWRS water undergoes constant, rigorous testing before being released back into the environment.  It exceeds all state and federal drinking water standards. The project was reviewed, approved and permitted by the California Department of Public Health and California Regional Water Quality Control Board, Santa Ana River Basin, to ensure public health, water quality and environmental compliance before allowing injection along the coast (approval received on January 10, 2008) and percolation into deep aquifers (approval received on January 18, 2008).

The permits require continuous water quality testing and sampling.  If the water does not meet water quality requirements, the plant would be shut down immediately.  The permit establishes criteria for the GWRS treatment, Total Organic Compounds (TOC) limits, and travel time and blending requirements.

One of the provisions of the permit requires that an Independent Advisory Panel (the Panel) provide an on-going periodic scientific peer review of the GWRS. The permit specifies minimum qualifications for the Panel members and requires that the Panel meet at least annually during the first five years, and then every two years thereafter. The Panel is appointed and administered by the National Water Research Institute (NWRI), and made up of experts in toxicology, chemistry, microbiology, hydrogeology, environmental engineering, public health and water treatment technology.

Yes.  OCWD tests for more than 400 compounds. All test results are well below permit levels or at non-detection (ND) levels. For example: 28 Volatile Organic Compounds – All ND; 39 Non-Volatile Synthetic Organic Compounds – All ND; 8 Disinfection By-Products – All ND; 10 Unregulated Chemicals – All but one ND, all are below permit levels; 51 Priority Pollutants – All ND; 16 Endocrine Disrupting Chemicals and Pharmaceuticals – All ND.

The California Department of Public Health and the Santa Ana Regional Water Quality Control Board, Santa Ana River Basin review water quality reports and have final approval of the production and distribution of GWRS water.

The California Department of Public Health (DPH) approval stipulates a 2-year phased approach of blending GWRS water for the seawater barrier. The blend is 75% recycled water with 25% dilution water. That permit requirement for the seawater barrier was lifted in 2010.  The blending requirement is still in place for the GWRS water that is pumped to the recharge basins. This measure is only precautionary since all water quality reports have been and continue to validate that the GWRS creates water of the highest quality that exceeds all state and federal drinking water standards.

Assembly bill 2022, which went into affect in January 2017, allows for the bottling of advanced purified wastewater (such as GWRS water) for educational purposes. OCWD and OCSD toured the state in 2017, bringing bottled GWRS water to the public.

Yes. The GWRS was built to allow for two expansions. The first, completed in 2015, expanded the project from 70 million gallons (265,000 cubic meters) per day to 100 million gallons (379,000 cubic meters; 307 acre-feet) per day. Construction of the GWRS Final Expansion began in 2019 and will be completed by 2023. Once complete, the GWRS will produce an additional 30 million gallons per day of drought-proof water to replenish the Orange County Groundwater Basin. The expansion will bring total GWRS production to 130 million gallons per day (492,000 cubic meters); enough water for one million people. For additional information, visit the GWRS Final Expansion webpage.

The two agencies are physically located next to each other in Fountain Valley, California. This proximity has many financial and logistical benefits. For more than 30 years, the two agencies have collaborated to solve water issues.  In 1976, to protect the basin from further seawater intrusion, the Orange County Water District (OCWD) initially constructed the internationally-known Water Factory 21 (WF-21).  WF-21 treated wastewater utilizing a state-of-the-art purification process that included reverse osmosis.  The WF-21 water was injected into 23 multi-casing injection wells along the Talbert Gap.  Injection in these wells formed a hydraulic barrier to seawater intrusion.  This mound of fresh water near the coast allowed for seasonal fluctuations in the aquifers landward of the barrier without the risk of seawater intrusion and its associated salt water contamination.

WF-21 was a first-of-its-kind, water recycling facility that helped pave the way for many international projects and ultimately the Groundwater Replenishment System (GWRS).  Since the 1970s, OC San has been supplying treated wastewater to OCWD at no cost. Both agencies were equal partners in the construction of the GWRS.

The projected cost for OC San to build a second ocean outfall was $200 million; less than the amount OC San ultimately invested to build the GWRS. Its GWRS contribution was $194 million.

OC San is responsible for wastewater collection, source control and treatment and disposal of wastewater for north and central Orange County. It operates the third-largest wastewater agency west of the Mississippi River.  Each day, OC San treats approximately 220 million gallons of wastewater – enough to fill Angel Stadium nearly three times each day. OC San facilities include 580 miles of sewer pipelines and two treatment plants.