Regional Recycled Water Program

Regional Recycled Water Program

Expanding Local Resources 

Water is too precious to use just once. So, the Metropolitan Water District of Southern California is making a major investment in a potential water recycling project that will reuse water currently sent to the ocean. 

The Regional Recycled Water Program will purify wastewater to produce sustainable, high-quality water that could be used again. This partnership with Los Angeles County Sanitation Districts started with a demonstration facility and could eventually become one of the largest advanced water treatment plants in the world.


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Starting Small & Scaling Up


The Advanced Purification Center is a 0.5 million gallon per day demonstration facility that will generate information needed for the potential future construction of a full-scale recycled water plant. It uses a unique application of membrane bioreactors designed to significantly increase efficiency in water recycling. Scientists and engineers are testing the process, utilizing full-scale treatment modules, to ensure the resulting purified water meets the highest water quality standards. Once approved by regulators, this innovative process could be used throughout California and even applied around the globe.


A full-scale regional recycled water program would produce up to 150 million gallons daily, enough to serve more than 500,000 homes. Purified water from the advanced treatment facility would be delivered through up to 60 miles of new pipelines to the region’s groundwater basins, industrial facilities and two of Metropolitan’s treatment plants.

Demonstration Facility
Full-Scale Program

How It Works

The process begins with wastewater discharged from homes, businesses and industries. After the wastewater has been cleaned and treated, it flows to an advanced water treatment plant where it is further purified. The water then replenishes groundwater basins and is eventually pumped up, disinfected and used again. It could also be delivered to industrial facilities and potentially to Metropolitan’s water treatment plants and delivery system.

Regional Recycled Water Process

The Process to Purification 

After wastewater is cleaned and treated through multiple processes, it flows to the Regional Recycled Water Advanced Purification Center where it goes through a three-step purification process. The end result is high quality, purified water that is safe to reuse again.


Membrane Bioreactors

Microorganisms remove ammonia and other nitrogen compounds, while membranes filter tiny particles, smaller than 1/100 of a grain of sand.


Reverse Osmosis

Pressurized membranes further remove microscopic materials, such as bacteria, pharmaceuticals and salts, eliminating more than 99 percent of all impurities.


Ultraviolet/Advanced Oxidation Process

Ultraviolet light and a powerful oxidant destroy any remaining viruses and trace chemical compounds.

Project Benefits

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Prepares the Southland for the event of a catastrophic earthquake by increasing local water supplies

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Produces a drought-proof source of water, readily available rain or shine

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Replenishes groundwater basins, which provide 30% of Southern California's water supply and have seen levels drop to historic lows in recent years

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Helps meet needs of region’s growing economy and population at a cost comparable to other local water resources

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Uses region’s largest untapped source of wastewater, currently sent to the ocean

Milestones in Recycled Water Use

The past five decades have seen recycled water use in Southern California grow rapidly, for both irrigation and groundwater replenishment.

Here's a look at its history in the region, from the first recycled water plant to the large recycling water projects we see today.



The Sanitation Districts’ Whittier Narrows Water Reclamation Plant becomes the first plant in the U.S. intentionally designed to recycle water, using it to recharge groundwater basins.



As Southern California’s population grows, recycled water lines are constructed alongside new development to irrigate schoolyards, parks and golf courses.



Water Factory 21 begins purifying wastewater in Orange County and using it to replenish and protect groundwater from seawater intrusion. Becomes first plant in the world to use reverse osmosis.



Wastewater treatment plants add processes to produce more recycled water. Purple pipes are adopted as industry standard to distinguish recycled water for irrigation, firefighting and industrial use.


1995 to 2005

Several new water recycling facilities are built that use reverse osmosis. The resulting water is used for groundwater recharge and industrial use.



Orange County embarks on the largest water reuse project of its kind in the world, eventually purifying 130 million gallons of water daily to replenish groundwater supplies used for drinking. Becomes the gold standard for water recycling.



The city of San Diego advances a water recycling program that for the first time in California would use purified recycled water to fill a drinking water reservoir.



Water agencies from Ventura to San Diego continue to take steps toward implementing large recycling projects. The Regional Recycled Water Program will take the rapid growth of recycled water use in Southern California even farther.

Growth recycled water
Laptop with virtual tour on screen

About the Partners

The Metropolitan Water District of Southern California is a state-established cooperative of 26 cities and water agencies serving nearly 19 million people in six counties. The district imports water from the Colorado River and Northern California to supplement local supplies, and helps its members to develop increased water conservation, recycling, storage and other resource management programs.

Los Angeles County Sanitation Districts are a regional public agency consisting of 24 independent special districts serving over 5.6 million people in 78 cities and the unincorporated territory within Los Angeles County. The Sanitation Districts protect public health and the environment through innovative and cost-effective wastewater and solid waste management and, in doing so, convert waste into resources such as recycled water, energy and recycled materials. The Sanitation Districts operate 11 wastewater treatment plants.  The Joint Water Pollution Control Plant in Carson is the largest of these plants and one of the largest in the country. Read more about the Joint Water Pollution Control Plant.

Awards & Recognitions

  • American Society of Civil Engineers Region 9 2021 Outstanding Water/Wastewater Project
  • Engineering News Record California 2020 Owner of the Year
  • Environmental Communications Award Grand Prize from the American Academy of Environmental Engineers and Scientists
  • Recipient, WaterSMART: Water Reclamation and Reuse Research Grant, U.S. Department of the Interior Bureau of Reclamation
  • $1 million Recycled Water Project Grant, State Water Resources Control Board 

Regional Recycled Water Advanced Purification Center: An Overview

May 18, 2021

Demonstration Facility Purification Process: Step 2

July 27, 2020

Demonstration Facility Purification Process: Step 1

July 27, 2020

Watch a recap of the launch of the facility

Nov. 5, 2019

Demonstration Facility Construction Progress as of September 2019

Sept. 30, 2019

Demonstration Facility Purification Process:  Step 3

April 29, 2019

Thinking Big: An Overview of the Regional Recycled Water Program

Dec. 7, 2018

Groundbreaking Event

Sept. 26, 2017

Technical Resources

Advisory Panels 

Independent Science Advisory Panel: Demonstration Project

The Advanced Purification Center is a demonstration facility that uses a unique application of membrane bioreactors in the advanced water treatment process. This demonstration facility will be used to evaluate the performance of the membrane bioreactors with reverse osmosis and an ultraviolet/advanced oxidation process. The project will also develop design criteria for a potential full-scale facility, clarify costs for advanced treatment, and ultimately obtain regulatory permits for a full-scale program.

An independent science advisory panel has been selected to provide an objective review of technical, scientific, regulatory, and public health aspects of the Advanced Purification Center. To ensure objectivity, the National Water Research Institute NWRI, a nonprofit organization with extensive experience in the water reuse industry, selected the panel and will manage its activities. The panelists represent industry and academic experts in drinking water treatment, wastewater treatment, advanced water treatment, toxicology, chemistry, microbiology, hydrogeology, pipeline corrosion, and drinking water and recycled water regulations and permitting. The panelists are listed below with their areas of expertise.

Regional Recycled Water Supply Program Advisory Panel, pictured from left: Ed Means (Panel Facilitator), Adam Olivieri, Nancy Love, Charles Haas, Vernon Snoeyink, Paul Westerhoff, Richard Bull (previous member), Joe Cotruvo, Thomas Harder, Paul Anderson (not pictured).



Paul Anderson, Ph.D.: Adjunct Professor, Center for Energy and Environmental Studies, Geography Department, Boston University. Dr. Anderson has been involved in toxicological research for more than 25 years. His expertise is toxicology.

Joe Cotruvo, Ph.D.: President of Joseph Cotruvo and Associates, LLC. Dr. Cotruvo has more than 45 years of experience conducting research and writing policy related to drinking water quality. His expertise is chemistry.

Charles Haas, Ph.D.: Betz Chair, Professor of Environmental Engineering & Head, Department of Civil, Architectural and Environmental Engineering, Drexel University. Dr. Haas has more than 45 years of experience conducting research. His expertise is microbiology.

Thomas Harder: Principal, Thomas Harder and Company Groundwater Consulting. Mr. Harder has more than 22 years of professional groundwater consulting experience. His expertise is hydrogeology.

Nancy Love, Ph. D.: Borchardt and Glysson Collegiate Professor, Department of Civil and Environmental Engineering, University of Michigan. Her research evaluates the fate and removal of pathogens and contaminants of emerging concern in water with relevance to public health and the environment and advances technologies that recover useful resources from water.

Adam Olivieri, Ph. D.: Principal/Founder, EOA Inc. Dr. Olivieri has over 30 years of experience in leading technical and regulatory projects associated with wastewater, water recycling and reuse, and others. His expertise is water regulations and permitting.

Vernon Snoeyink, Ph. D.: Professor Emeritus at the University of Illinois. Dr. Snoeyink’s research career has focused on aquatic chemistry and corrosion control, focusing on drinking water distribution systems. His expertise is pipeline corrosion.

Paul Westerhoff, Ph.D.: Regents Professor, School of Sustainable Engineering and The Built Environment, Arizona State University. Dr. Westerhoff has taught at Arizona State University since 1995. His expertise is drinking water treatment and advanced water treatment.

The independent science advisory panel will participate throughout the testing period for the demonstration project and until report(s) are submitted to regulators for approval of the purification process.

The independent science advisory panel is the second panel for the Regional Recycled Water Program. Initially, an advisory panel was created to provide input on the feasibility of the program. 

Advisory Panel: Feasibility Study 

Metropolitan and Los Angeles County Sanitation Districts are working collaboratively to develop a potential regional recycled water supply program that would purify and reuse water for recharge of groundwater basins in Southern California. An advisory panel of key subject matter experts was established to provide independent review and critical input on the scope and direction of the program during its demonstration project phase. In this initial effort, the panel provided input into the development of the program's feasibility and financial assessments, as well as the design of the demonstration plant.


Pictured, from left: Ed Means, Joe Reichenberger, Richard Atwater, Thomas Harder, Paul Westerhoff, David Jenkins, Shivaji Deshmukh, Margie Nellor (not pictured).



Margie Nellor, Co-Chair: Expert on recycled water reuse programs, pretreatment and related regulatory issues.

Richard Atwater, Co-Chair: Expert in recycled water programs and past Executive Director of Southern California Water Committee.

Shivaji Deshmukh: West Basin Municipal Water District, Assistant GM with recycled water engineering and operational experience with Advanced Water Treatment facilities at both the West Basin Water Recycling Facility and the Groundwater Replenishment System in Orange County.

Thomas Harder: Hydrogeologist with expertise on Southern California's groundwater basins.

David Jenkins: Professor Emeritus of Civil and Environmental Engineering at UC Berkeley, with expertise on biological wastewater treatment processes, and water and wastewater chemistry (passed away March 2021).

Ed Means: Internationally recognized water quality and water resources management expert, with over 35 years experience, numerous peer-reviewed publications, and contributor or author of several books.

Joe Reichenberger: Professor at Loyola Marymount University, Professional Engineer and Board Certified Environmental Engineer, with over 50 years experience in water, wastewater and recycled water systems and treatment.

Paul Westerhoff: Professor at Arizona State University with expertise in advanced treatment processes.

The panel met periodically to review and discuss selected topics presented by project staff. These reviews provided input on:

  • Overall program feasibility and work plans,
  • Conceptual design of the Demonstration Plant,
  • Ideas and approaches to program implementation, and
  • Development of program options and alternatives.


Frequently Asked Questions 

Read answers to frequently asked questions. Contact us for additional information.

The Regional Recycled Water Advanced Purification Center (Center) is a 500,000 gallon-per-day demonstration facility designed to test an innovative water purification process for potential groundwater replenishment. Cleaned wastewater from the Los Angeles County Sanitation Districts’ (LACSD) Joint Water Pollution Control Plant (JWPCP) in Carson is sent to the Center, where it is further purified using a unique application of membrane bioreactors followed by reverse osmosis and an ultraviolet light/advanced oxidation process. Scientists and engineers are testing this advanced purification process to demonstrate that the resulting purified water meets all health and water quality requirements and is safe to replenish groundwater basins used as a drinking water supply. As it is a testing facility, the water purified at the Center goes back to the start of the JWPCP to be re-treated and eventually sent to the ocean.

The Center tests a potential purification process for the Regional Recycled Water Program to ensure it produces water safe for groundwater replenishment and reuse. A key objective of the facility is to obtain regulatory approval for the innovative purification technology in use. It also allows Metropolitan, in collaboration with LACSD, to optimize operations and identify costs, gather operational data, and develop design parameters needed for a future full-scale facility. In addition, the Center is used to showcase the project to the public. Visitors have an opportunity to virtually tour the facility and learn more about the purification process.

No. While recycled water in purple pipe systems undergoes an extensive treatment process and can be used for irrigation and industrial purposes, the water is not intended for human consumption. The Center uses advanced water treatment technologies such as reverse osmosis and ultraviolet disinfection, which have been used in Southern California and elsewhere for decades to produce water that safely replenishes groundwater basins for use as a drinking water supply.

Ocean desalination also uses reverse osmosis technology. However, because ocean water is about 25 times saltier than wastewater, desalination requires much more energy, additional membranes, and higher operational and maintenance costs compared to purifying wastewater.

Yes, the technologies in the purification process at the Center remove pharmaceuticals and other microscopic materials. This has been verified at the Center, in previous pilot studies conducted by Metropolitan and LACSD, and by water agencies operating purification facilities that use some of the same advanced technological processes. The purified water is monitored and tested by scientists and engineers for hundreds of compounds, including pharmaceuticals, to ensure the water meets water quality requirements to replenish groundwater basins.

Membrane bioreactors (MBR) are often used in wastewater treatment plants, where they remove organic materials and nitrogen compounds from water. At the Center, the MBR uses both biological treatment and membrane technology to clean the water before it is sent on the reverse osmosis process. The Center’s MBR serves two purposes. First, it removes nitrogen compounds from the water through biological treatment. Second, it filters particles – many smaller than 1/100th of a grain of sand – using membrane technology. The MBR process ensures that the reverse osmosis units operate successfully without fouling, or prematurely downgrading, them.

The JWPCP is an ocean discharge facility and not designed to remove nitrogen compounds such as ammonia, nitrates and nitrites from wastewater. The Center’s purification process must remove these and other compounds to ensure the water is safe to replenish groundwater basins. MBRs are not only effective at removing nitrogen compounds, but also are able to remove organics and other microscopic materials, including microorganisms such as Cryptosporidium and Giardia. In addition, they help minimize the fouling and downgrading of reverse osmosis membranes. Microfiltration alone cannot perform this important two-step treatment process of removing nitrogen and removing particulates from the water prior to reverse osmosis treatment. While MBRs have been extensively used in wastewater treatment, they have not yet been tested for groundwater replenishment projects in California. If the MBR technology, in combination with reverse osmosis and an ultraviolet light/advanced oxidation process (UV/AOP), is able to achieve the same level of performance as using microfiltration with reverse osmosis and UV/AOP, it could result in increased efficiency and significant cost savings for water reuse projects.

Potable water is drinkable. Potable reuse refers to highly purified water that meets or exceeds federal and state drinking water standards and is safe to reuse for drinking. The Center is currently focused on producing purified water for indirect potable reuse, i.e. water that doesn’t flow directly to a user. With indirect potable reuse, purified water would first replenish groundwater basins, where it would undergo additional, natural filtration and blend with other water supplies. Water from the underground basin would eventually be pumped up, treated, and reused again.

Direct potable reuse refers to purified water that flows directly into the drinking water treatment and distribution system, skipping the groundwater basin step. Metropolitan is considering direct potable reuse where purified recycled water would be an additional supply added upstream of the water treatment process. This is called raw water augmentation and regulations for this type of reuse are expected to be released in 2023. Purification processes for raw water augmentation may be tested in the future at the Center.

The testing period involves three stages: (1) initial testing of equipment and developing laboratory methods; (2) testing each technology and the overall purification process for performance during normal, baseline conditions; and (3) testing each technology and the overall purification process for performance during compromised or challenged conditions. Currently, the third stage of testing is in implementation. During the testing period, scientists and engineers evaluate and monitor the purification process for hundreds of water quality parameters to determine its ability to produce water that complies with all water quality and regulatory requirements associated with groundwater replenishment and reuse. Final testing results are expected in late 2021.

After the testing period is complete, Metropolitan will prepare a detailed report on the demonstration project, including water quality data and test results and submit it to the State Water Resources Control Board’s Division of Drinking Water (Division) for review. The Division will determine if the proposed purification process, including application of the MBR technology, meets all water quality and public health standards. The report also will be submitted to the Los Angeles and Santa Ana Regional Water Quality Control Boards to ensure all water reuse requirements are met. Once the purification process is approved, it may be used for a future full-scale facility. This efficient, cost-effective advanced treatment process also may be used by other water utilities, further expanding water reuse in California.

Extensive testing is conducted at the Center to demonstrate the purification process using MBR technology will meet regulatory requirements. Ultimately, if the purification process is not approved, other alternatives will be considered. One option would be to be to use MBRs or potentially another nitrogen removal technology in addition to the purification process used at existing facilities (microfiltration, reverse osmosis, UV/AOP). Other options also would be researched and reviewed as needed.

Once testing is complete, the Center may be used to conduct additional studies on membrane bioreactors in the water purification process. Specifically, Metropolitan and LACSD will evaluate using MBRs as a part of the wastewater treatment process as another option for this project. These studies will provide information needed to further develop the design and operations of a full-scale advanced water treatment facility. Additional research and treatment evaluations also may be conducted in the future for other types of reuse, such as direct potable reuse via raw water augmentation, in which the purified water flows directly into one of Metropolitan’s water treatment plants and then into the distribution system instead of to a groundwater basin. New regulations for this type of process are expected to be released in 2023.

Currently, virtual tours are available. For more information and to register, please visit our Tours webpage.

During the testing period, no water tasting will take place because the Center’s purification process has not yet been approved by regulators. After the process is approved, there may be opportunities to taste the purified water.

During the testing period, the purified water from the Center returns to the start of the JWPCP where it is re-treated and eventually flows to the ocean. If a full-scale program moves forward, the purified water could recharge groundwater basins in Southern California, be used by industries, and potentially, as regulations are developed, provide another source of water to two of Metropolitan’s water treatment plants.

Metropolitan’s budget includes both capital and operations and maintenance costs for the Center. LACSD, partners in the demonstration project, have provided critical infrastructure and services such the project site, electrical power, process water piping, staff time and various resources to perform laboratory analyses.

Metropolitan is researching grant and other funding opportunities at the state and federal levels for both the demonstration facility and a full-scale program. To date, Metropolitan has received nearly $3 million in grants from the U.S. Bureau of Reclamation and the State Water Resources Control Board.

In November 2020, both the Metropolitan and LACSD Boards of Directors gave approval to begin the environmental planning phase for the Regional Recycled Water Program. This phase will take place from 2021-2024 and includes technical studies and environmental analyses that will provide additional information about the program. Once environmental documentation is complete, the agencies’ boards will consider approval of final design and construction for the project. If approved, the full-scale project will take seven years to complete and the program would be begin in 2032.

The program will require environmental evaluation and review in accordance with the California Environmental Quality Act (CEQA). Metropolitan is planning to develop a Program Environmental Report (PEIR)to meet these requirements. A PEIR is a type of CEQA document designed to be used for large programs/projects with multiple components that require multiple agency approvals or multiple construction contracts. As design elements of the program progress, future assessments will be made to determine whether additional environmental documentation, beyond the original PEIR, must be prepared.

Currently, a full-scale program producing up to 150 million gallons of water each day is estimated to cost $3.4 billion to build and $129 million each year to operate and maintain, resulting in a total cost of about $1,830 per acre-foot of purified water.

The full-scale Regional Recycled Water Program would produce a drought-proof local source of water, readily available rain or shine, for Metropolitan’s service area. It would help free up imported water for other uses. The water also would help replenish Southern California’s groundwater basins, which provide 30 percent of the region’s water supply and have seen levels drop to historic lows in recent years. The water provided would help diversify the region’s water sources to meet the needs of the growing economy at a cost comparable to other local water resources.

If a full-scale program is constructed, the water could be used to refill up to four groundwater basins in Los Angeles and Orange counties. These basins supply water to 7.2 million people throughout these counties. The water could also be used by industries in the Harbor area. In addition, when regulations are developed allowing for it, the water could provide an additional source of water for Metropolitan’s Weymouth and Diemer water treatment plants, eventually delivering the water to much of Metropolitan's service area. Other opportunities for use of the purified water may also be developed in the future.

Please visit our website for more information. You may also sign up for e-mail updates from Metropolitan about current programs and projects, including the Center.


Regional Recycled Water Program