Southern California has taken a major step forward on the path to developing a new sustainable water source from purified wastewater as Metropolitan Water District’s Board of Directors voted to begin environmental planning work on what would be one of the largest advanced water treatment plants in the world.

The approval marks a significant milestone for the Regional Recycled Water Program, a partnership between Metropolitan and the Los Angeles County Sanitation Districts to reuse water currently sent to the ocean.

“Our board has shown over the past five years that we are committed to creating a drought-proof, local water supply for the region by investing in this project,” Metropolitan Board Chairwoman Gloria Gray says. “We all recognize our growing duty to ensure Southern California has reliable water in the face of threats from climate change and earthquakes. This project builds that resilience.”

If fully realized, the project would take cleaned wastewater from the Los Angeles County Sanitation Districts’ Joint Water Pollution Control Plant in Carson and purify it using innovative treatment processes, producing up to 150 mgd — the amount used by more than 500,000 homes.

The purified water would initially be used for groundwater replenishment and storage, and by industrial facilities. After additional treatment, it may later be delivered directly to Metropolitan’s existing water treatment plants and used for drinking water, after the state develops regulations for direct potable reuse.

The board’s recent vote allows Metropolitan to initiate the necessary environmental planning work, including a Program Environmental Impact Report, engineering and technical studies, and to continue public outreach. This work will cost about $30 million and take approximately three years.

“The information produced will be critical to provide our board with the necessary information to make a fully informed decision in 2024 whether to build this project,” Metropolitan General Manager Jeffrey Kightlinger says. “When combined with our investments to ensure the reliability of our imported supplies from the Colorado River and the northern Sierras, we can build water security for the region for generations to come.

“Metropolitan has never before directly developed a local supply like this. It is a huge opportunity for Southern California, and an opportunity that can only succeed through a partnership between two large regional agencies like Metropolitan and the sanitation districts.”

At their upcoming meeting, the Los Angeles Sanitation Districts Board will consider contributing approximately $5 million toward the environmental planning costs, along with undertaking additional studies to support the project, through an agreement also approved by Metropolitan’s board.

The recent vote marks Metropolitan’s latest investment in the Regional Recycled Water Program. Last year, Metropolitan launched a $17 million demonstration plant to test an innovative purification process that could be used in a full-scale plant. Though that process is based on proven technologies, it uses a new combination of treatment processes — starting with membrane bioreactors and followed by reverse osmosis, ultraviolet light and advanced oxidation — that could significantly increase efficiencies in treatment.