Pure Water Southern California

Regional Recycled Water Program

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 program that would reuse water currently sent to the ocean. Pure Water Southern California, formerly known as the Regional Recycled Water Program, will take cleaned wastewater and further purify it to produce a new, sustainable source of high-quality water for Southern California.

This partnership with the Los Angeles County Sanitation Districts would produce up to 150 million gallons of water daily when completed and provide purified water for up to 1.5 million people, making it one of the largest water reuse programs in the world.


Pure Water Southern California’s Environmental Review Process

The next major step in the Pure Water Southern California program is completing its environmental review. The environmental review process allows Metropolitan and the Los Angeles County Sanitation Districts to explore and understand the project’s potential impacts to communities and the environment.


Steps in the Environmental Review Process

During the environmental review process Metropolitan and the Sanitation Districts will prepare an Environmental Impact Report (EIR). Development of the EIR includes three phases and public involvement opportunities.


1. Scoping Phase: Complete 

The first part of the environmental review process is the scoping phase, which is initiated by a Notice of Preparation that tells public agencies and interested parties that an Environmental Impact Report will be prepared. Feedback is encouraged to help identify environmental issues and raise questions and concerns for further study in the EIR.  Project alternatives, community impacts and mitigation measures also are considered.

2. Draft EIR Release: First Quarter 2024

The Draft EIR will be available for public review to allow community members, interested parties and agencies the opportunity to provide feedback and comments.  Metropolitan staff will review comments, prepare responses, and revise the EIR as needed.

3. Final EIR Certification: Fall 2024

The Metropolitan Board of Directors will review and consider certification of the Final EIR during a board meeting, which will be open to the public.

“The best science tells us that we need to act now to adapt to California’s water future.”

Gov. Gavin Newsom

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About the

Think of it as a living laboratory. The Pure Water Southern California Demonstration Plant, which began operation in October 2019, is generating information that can be used if plans for a full-scale advanced water purification facility move forward in the future. One of the main purposes for the plant is to facilitate regulatory approval of the innovative purification technology being used.

Here, scientists and engineers test the purification process with full-scale modules, to be sure that the purified water produced meets the highest water quality standards. This means that it is safe to replenish groundwater basins that are used as a drinking water supply source.

During the demonstration phase, the water purified at the plant goes back to the Los Angeles County Sanitation District’s Joint Water Pollution Control Plant in Carson where it is retreated and eventually released to the ocean. If the project moves to full scale, the purified water would be transported up to 60 miles through a new network of pipelines to Southern California groundwater basins, industrial facilities and potentially water treatment plants.

Today, the demonstration plant treats 500,000 gallons per day using a unique application of membrane bioreactors to purify the water. That is followed by reverse osmosis and an ultraviolet light/advanced oxidation process. At full scale, the plant would treat 150 million gallons daily – enough for about 500,000 homes. The technology used, once approved by regulators, could be applied in the state and even globally.

A Look Inside How It Works

The Pure Water demonstration facility uses a 3-step purification process. The first step involves membrane bioreactors, the second step is reverse osmosis, and the third step is ultraviolet disinfection and advanced oxidation. What makes this treatment process innovative is the use of MBRs in water reuse treatment. They have been used in the wastewater industry for decades but are new to the world of water reuse. Their effectiveness also has been studied internationally in countries like Australia and Singapore, where the technology effectively purified water for eventual consumption. The MBRs are able to remove materials dissolved in water like organic matter, nitrogen and other particles down to a microscopic level. Their eventual use in the purification process, once granted regulatory approval, is what makes the Pure Water process innovative.

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The Purification Process

Membrane Bioreactors

Membrane bioreactors use biological processes and membrane technology to clean water.

Air is added to biological process tanks to create an environment where helpful microorganisms thrive. The microorganisms remove organic material and nitrogen compounds, such as ammonia and nitrate.

The water flows into membrane tanks where thousands of straw-shaped membranes with tiny pores filter and remove microscopic materials, including microorganisms and other particles. Many are smaller than 1/100 of a grain of sand.

Reverse Osmosis

Reverse osmosis is often considered the core water purification process and eliminates more than 99% of all impurities. Water leaving the MBRs is pressurized with a series of pumps and applied to tightly wound membranes, which selectively allow water molecules through the membranes’ pores, while blocking the passage of microscopic materials, such as bacteria, pharmaceuticals and salts.

Reverse osmosis is widely used to purify water, most commonly to remove salt in seawater desalination projects. It is also used in many bottled water processes and groundwater replenishment projects.

Ultraviolet Light/Advanced Oxidation

Ultraviolet light is a powerful disinfectant used to inactivate viruses in water. When ultraviolet light is combined with a strong oxidant, either hydrogen peroxide or sodium hypochlorite, extremely reactive molecules are created. These molecules remove trace chemical compounds that may remain. The combination of the ultraviolet light and strong oxidant is referred to as the Advanced Oxidation Process. This is a final polishing step that ensures the water is safe and highly purified.

Demonstration Plant Tours

Take a tour of the Pure Water Southern California Demonstration Plant to learn more about the facility, its innovative purification process and the importance of purified, recycled water to Southern California’s future water supply. Tours also are available in Spanish.


Learn More

Over a Decade
in the Making

Since the early 1960s, the Los Angeles County Sanitation Districts have operated plants designed to recycle water used to replenish groundwater basins, our natural underground water reservoirs. Since the early 1980s, Metropolitan has supported new local supply project development by its member agencies, including recycling projects. Until now, Metropolitan has never had a water recycling project of its own, but through a partnership, the two agencies are collaborating on what could set global precedent as one of the largest water reuse programs. 

This large-scale program requires many collaborators, and Pure Water Southern California has many partners, including groundwater basin managers, other Metropolitan member agencies and even water agencies in Arizona and Nevada.  The shared goal is to create a sustainable water future that balances local water resources with imported supplies from the Colorado River and the State Water Project, which are experiencing unprecedented shortage conditions due to drought.

Innovation at Work

Pure Water Southern California is novel in its scale and purification process, but the concept of recycling water is not new.  Several communities across Southern California, including some in Los Angeles, Orange and San Bernardino counties, - not to mention uses worldwide - use recycled water for drinking and other applications.

Click on the to explore various innovative programs in development and operation throughout our region.


Pure Water San Diego

City of San Diego
San Diego, CA

The City of San Diego is constructing a new water recycling plant and associated facilities to produce 30 million gallons of purified water daily. This is the first phase in its multi-year Pure Water Program that will provide one-third of the City’s water supply by 2035.


Edward C. Little Water Recycling Facility

West Basin Municipal Water District
El Segundo, CA

The Edward C. Little Water Recycling Facility purifies water from the City of Los Angeles' Hyperion Wastewater Treatment Plant and produces water for irrigation water, industrial use, and adding to groundwater to prevent seawater intrusion.


Groundwater Replenishment System

Orange County Water District
Fountain Valley, CA

The Groundwater Replenishment System is the world's largest advanced water purification system. The system produces 100 million gallons of purified water daily to help refill groundwater basins. It is currently undergoing an expansion to 130 million gallons daily.


Albert Robles Center for Water Recycling and Environmental Learning

Water Replenishment District
Pico Rivera, CA

The Albert Robles Center purifies and recycles approximately 14.8 million gallons of water daily, which is used for groundwater replenishment. The Center is a multipurpose and multi-benefit site which includes an Advanced Water Treatment Facility, a fully digital Learning Center, and a water-efficient Demonstration Garden.


Pure Water Oceanside

City of Oceanside
Oceanside, CA

Pure Water Oceanside is an advanced water purification program that purifies recycled water to create a new, local source of drinking water. Between 3 to 5 million gallons of drinking water is created each day, enough to provide 32% of the City of Oceanside’s water supply.


EMWD Recycled Water Program

Eastern Municipal Water District
Riverside County, CA

Recycled water makes up more than one-third of Eastern Municipal Water District’s water supply portfolio. Recycled water is used for agriculture, irrigation and industrial use. EMWD is also planning to produce purified recycled water for groundwater replenishment through its Purified Water Replenishment program.


Aquifer Storage Recovery Project

City of Oxnard
Oxnard, CA

The City of Oxnard’s Advanced Water Purification Facility produces recycled water for irrigation of parks, medians, golf courses and athletic fields; watering of agriculture crops; and process water for local industries. The City plans to expand its facility and use recycled water for groundwater replenishment.


Recycled Water & Chino Basin Program

Inland Empire Utility Agency
Chino, CA

IEUA receives and cleans more than 50 million gallons per day of wastewater, which is then used for agriculture, municipal irrigation, industrial uses, and for groundwater replenishment. IEUA is also planning to provide additional purified recycled water for groundwater replenishment by 2028.


East County Advanced Water Purification

Padre Dam Municipal Water District
East San Diego County, CA

The East County Advanced Water Purification Program will create a new drinking water supply utilizing state-of-the-art technology to recycle the region’s wastewater. The project is under construction and scheduled to be online in 2025.


Water Reclamation Plants

Los Angeles County Sanitation Districts
Whittier, CA

The Los Angeles County Sanitation Districts began replenishing groundwater with recycled water in 1962 at their Whittier Narrows Water Reclamation Plant. Recycling has since expanded to 10 treatment plants and they have recycled over 1 trillion gallons.


Environmental Review Documents and Resources

Watch a recording from a past virtual community meeting: 

Meeting in English

Meeting in Spanish

Watch a video to learn how to participate.

English version:

Watch the Scoping Participation Video

Spanish version:

Vea el vídeo sobre cómo participar durante la fase de alcance

Check out our guide for submitting scoping comments here.

Spanish translation

Tagalog translation

Khmer translation


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: Phase I

April 29, 2022

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 Pure Water Southern California Demonstration Plant is a 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.

PWSC advisory Panel 2 Demo

Pure Water Southern California 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.

RRWP advisory Panel Feasibility

Pure Water Southern California Advisory Panel, 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.


Pure Water Southern California