South Bay water provider West Basin Municipal Water District (West Basin) is investing in its infrastructure to maximize the use of recycled water and reduce the reliance on imported water. One example is West Basin’s recent Phase II Expansion of the Juanita Millender-McDonald Carson Regional Water Recycling Plant, which underscores this effort and ingenuity within the water industry.

The project included an expansive upgrade of its previous microfiltration system to a custom-engineered microfiltration (CEMF) system that treats nearly 6 million gallons per day. The new CEMF system greatly increases its capacity and improves the reliability of the recycled water that West Basin delivers to Marathon Petroleum’s Los Angeles Refinery (Marathon). The water recycling plant’s microfiltration system can now fit six different membrane modules, which greatly improves the water-cleaning process. This results in greater recycled water production to meet West Basin’s sustainability and reliability goals.


  1. Full restoration and increase in the capacity of the reverse osmosis process—a water purification process that uses pressure to force water through a semipermeable membrane, removing contaminants and leaving behind clean water
  2. Improved system maintenance, operation and water quality
  3. Enhanced recycled water supply
  4. Construction of new on-site backup potable (drinkable) water
  5. Installation of a backup power supply for key operating equipment
  6. New ability to obtain cost-competitive pricing for future system equipment replacements
  7. Installation of systems to further improve water quality

Plant Upgrade Receives Global Recognition

Kevin Cullen, West Basin engineer (left), and Melene Agakanian, engineer at project partner Hazen and Sawyer, stand next to West Basin’s exhibit at the “Elevating Industrial Reuse: A California Example of Water Resiliency” poster session. It was featured at the 39th Annual WateReuse Symposium.

Further highlighting its impact, earlier this year in Denver, Colorado, the CEMF project was selected to be showcased at the 39th Annual WateReuse Symposium, the premier global conference on water recycling. The project exhibit at the symposium was entitled Elevating Industrial Reuse: A California Example of Water Resiliency. The project was widely and positively received by symposium attendees. For more information visit

West Basin also presented the project expansion at two conventions in 2023. This highlights the investments made by the district in collaboration with its partners at Marathon, the State Water Resources Control Board and Cal Water to further the message that “every drop of recycled water saves potable water for drinking and other essential uses.” •