California Regulator Adopts Rules for Converting Wastewater to Drinking Water

A worker climbs stairs among some of the 2,000 pressure vessels that will be used to convert seawater into fresh water through reverse osmosis in the Western Hemisphere's largest desalination plant in Carlsbad, Calif., on March 11, 2015. Gregory Bull/AP Photo

California regulators approved regulations on Dec. 19 that would enable water system agencies to establish treatment protocols for converting wastewater into high-quality drinking water.

The state Water Resources Control Board said that would allow water systems throughout the state to generate “a climate-resilient water source” while reducing the amount of wastewater released into rivers and the ocean.

“On top of helping us build drought-resilient water supplies, direct potable reuse offers energy savings and environmental benefits,” E. Joaquin Esquivel, chair of the Water Resources Control Board, said in a statement.

“Most importantly, these regulations ensure that the water produced is not only safe but purer than many drinking water sources we now rely on.”

The regulations were developed by the board over many years after an assessment by a panel of experts that the standards are protective of public health. A state law had required the board to approve these regulations by Dec. 31—a deadline met with just days to spare.

Darrin Polhemus, deputy director of the board’s division of drinking water, said the new rules require the wastewater to be treated for all pathogens and viruses, compared to regular water treatment rules, which require only treatment for known pathogens.

In addition, the treatment is so stringent that it eliminates all of the minerals that make fresh drinking water taste good—meaning that they have to be added back at the end of the process.

‘Critical New Tool’ for Water Managers

Sewage water is seen ponding near a storm drain at Venice Beach, near Santa Monica, Calif., one day after Tropical Storm Hilary made landfall, on Aug. 21, 2023. Courtesy of Soledad Ursúa

Adel Hagekhalil, general manager and CEO of the Metropolitan Water District of Southern California, said the new rules will give water managers “a critical new tool as we confront the challenges of climate change.”

“A portion of the purified water produced will be used for groundwater replenishment, while a portion will go through an additional DPR treatment process, then be delivered to one or two of our water treatment plants for further treatment and delivery across the region,” he said in a statement.

“This flexibility will allow us to ensure Southern California has a reliable water supply in dry years, while taking full advantage of water available in wet years.”

Mr. Hagekhalil said the new rules will help to advance large-scale water recycling projects that are currently in the works while enabling water managers “to consider new projects that have not yet been contemplated.”

“Water reuse will become an even more integral part of our state’s supply reliability,” he said.

The Metropolitan Water District of Southern California, which serves 19 million people, aims to produce up to 150 million gallons per day of recycled water. A project in San Diego aims to account for nearly half of the city’s water by 2035.

Water agencies will need public support to complete these projects—which means convincing customers not only that recycled water is safe to drink, but also that it isn’t disgusting.

The Associated Press contributed to this report.