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Is Water Recycling the Answer to the Bay Area's Drought Woes, Algae Blooms?

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A person holds a beaker of clear liquid with a label on it that reads "Purified Water."
Lakeisha Bryant, a spokesperson for Valley Water, holds a beaker filled with purified water at Silicon Valley Advanced Water Purification Center in San José on Aug. 14, 2023. The facility uses microfiltration, reverse osmosis and ultraviolet light to purify treated wastewater. (Beth LaBerge/KQED)

When recycled for drinking, the millions of gallons of water that Bay Area residents flush down toilets and showers every day could be cleaner than the pristine Hetch Hetchy water that flows from many taps in the region, according to a top California water official.

“Both are drinkable and pure,” said Darrin Polhemus, deputy director of the drinking water division of the state’s Water Resources Control Board. Recycled water for human consumption, he added, will be so clean that workers will have to add minerals to it, because the purification process strips the water of necessary minerals that make it drinkable.

But recycling the region’s used water for drinking, a process called “direct potable reuse,” is not happening anywhere in the Bay Area — at least not yet. Polhemus’ agency, however, is working to change that by drawing up rules for how local water agencies can pump ultra-purified water straight into the pipes that connect to people’s homes.


Water agencies that opt in early would either have to build entirely new water recycling plants, join forces with other water companies, or add water reuse capabilities to their operations. The entirely optional regulations could be official next year and, within half a decade, some agencies may be using the technique to help drought-proof their water portfolios.

“It’s going to be purified water that’s going to have the highest level of treatment ever, and it will be monitored at the beginning, middle and end of the purification process,” Polhemus said. “It is the highest treated water we’re ever going to produce in the state.”

Some water and climate experts believe recycling wastewater for human use is a climate adaptation strategy that, if employed wisely, could be a remedy for both future water shortages and the toxic algae blooms that have begun to perennially plague the San Francisco Bay.

“The impacts of climate change need solutions commensurate to the issue, and water recycling for human use is the reimagining we need,” said William Abraham Tarpeh, an assistant professor of chemical engineering at Stanford University.

A large room full of industrial equipment and a poster of a person holding a glass of clear water.
A photo hangs above the microfiltration systems at Silicon Valley Advanced Water Purification Center in San José on Aug. 14, 2023. (Beth LaBerge/KQED)

The purification process in a nutshell: Once soiled water swirls down the drain or toilet and reaches a wastewater plant or recycling facility, it is forced through a series of tiny tubes, pipes and filters and hit with ultraviolet light and other treatments like reverse osmosis and hydrogen peroxide, to strain and scrub out bacteria and parasites.

“It is beat up a lot. It’s the same technology used to desalinate ocean water,” said Lakeisha Bryant, a spokesperson for the Santa Clara Valley Water District, which operates the Silicon Valley Advanced Water Treatment Purification Center in San José. Similar to most other agencies in Northern California, the water purified in the facility is currently only used for things like landscape irrigation, cleaning buildings, industrial cooling, some agriculture and toilet flushing — but not human consumption. Some agencies even sell the recycled wastewater to oil refineries to generate steam to make fuel. Others hope to pump it deep into the earth to recharge depleted aquifers.

Valley Water aims to use recycled wastewater for at least 10% of the county’s total water demands by 2025, its website states.

And while none of that will be for human consumption, the agency is also attempting a small-scale pilot project to bottle water for human use over the next year in preparation for the new statewide rules.

A young Black woman standing in a factory holds a bottle of water.
Lakeisha Bryant, of Valley Water, samples a bottle of recycled water at Silicon Valley Advanced Water Purification Center in San José on Aug. 14, 2023. (Beth LaBerge/KQED)

“It will be good enough for people to drink, and that will be a huge game changer when it comes to public perception,” said Lei Hong, operations manager at the South Bay plant.

In addition to the state’s impending water recycling guidelines, another impending regulation, set to roll out next spring, will have far-reaching effects in the Bay Area. All 37 wastewater treatment plants across the region will be required, via a permitting process, to reduce the sheer volume of treated wastewater they pump into the bay.

The plethora of microscopic elements — like nitrogen and phosphorus — in that water is a smorgasbord for the single-tailed algae that darkened the water rusty brown in parts of the bay the past two summers, and last year killed thousands of fish.

More Stories on Algae Bloom

Eileen White, executive officer of the San Francisco Bay Regional Water Quality Control Board, which will issue the permits, said the new rules could force wastewater agencies to reduce their output of this algae food by as much as 50%, with the goal of eliminating the nutrient “buffet” that algae love feeding on.

That exact percentage, however, is still an open point of debate. White’s team is meeting with water agencies across the region and said they will use the best science to determine the exact percentage.

“We’re looking at very significant reductions given what occurred last summer,” she said.

Just 10% of all the water that flows into wastewater plants in the region today is recycled, White said, noting that while her board has encouraged local water agencies to increase their recycling capacity, there is currently no direct requirement to do so.

Lorien Fono, the executive director of the Bay Area Clean Water Agencies, which represents the five largest wastewater treatment agencies in the Bay Area, said there are significant barriers to turning wastewater into drinking water. The big one: price.

It can cost more than $1 billion to establish one water recycling project, a cost many agencies consider prohibitive, even with the help of available state and federal grants. Space for the new plants and jurisdictional issues are also major roadblocks. Only some wastewater agencies are water suppliers, so there would need to be collaboration across separate agencies and private companies.

“Recycled water is in its infancy in our region,” Fono said. She said the barriers, mostly cost and limited land, don’t make the Bay Area an ideal place for water recycling for human consumption.

For many agencies, geography is also a major limitation for expanding water recycling capacity.

A purple sign on a metal post reads, "Recycled Water in Use." Reeds and dead tan grass are behind it.
A sign says, ‘Recycled Water in Use’ outside of the Silicon Valley Advanced Water Purification Center in San José on Aug. 14, 2023. (Beth LaBerge/KQED)

Amit Mutsuddy, director of wastewater for the East Bay Utility District, whose plant is sandwiched between three freeways, said he doesn’t think direct potable reuse is a likely option because of the hefty price tag and limited space.

“We are landlocked, so we cannot expand,” he said, adding the agency is experimenting with other practices to decrease nutrients.

Mutsuddy’s site continuously pumps treated wastewater into the bay, several hundred feet from the shore, via a metal pipe 30 feet under the water. Much of that could be returned to the water supply, if recycling became a feasible option.

“This is an incredibly important moment,” said Meagan Mauter, a Stanford University environmental engineering professor, whose lab focuses, in part, on using renewable energy to meet the extensive power demands of wastewater treatment plants.

“We need to move towards the mentality that this is what the region needs to be thinking about in order to ensure the resiliency and affordability of our water supplies,” she said.


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