California poised to allow ‘toilet to tap’ projects, in landmark water rule

California water regulators are poised to approve long-awaited rules that will allow local water agencies to convert sewage — such as what drains from toilets and showers — directly into drinking water.

The landmark regulations will go before the State Water Resources Control Board for consideration next week. If approved, they would enable projects sometimes dubbed “toilet to tap” to move forward in numerous communities, including Santa Clara County, Los Angeles and San Diego.

Reusing water “gives us a supply that in essence is always going to be there,” said Darrin Polhemus, deputy director in the division of drinking water at the water board.

Additional options for drinking water are expected to become critical as climate change intensifies the risk of drought.

Right now, most wastewater in California gets treated and then discharged into the ocean, rivers or other bodies of water. Under the proposed rules, some water could be kept within the system — treated to a higher level and, in a matter of hours or days, returned to the main water supply, in a process known as direct potable reuse.

Because of the extra treatment, “It really will be some of the highest water quality available,” said Polhemus, who has himself tasted some recycled water at a project in Southern California.

A few other Western states, including Texas and Colorado, are also experimenting with direct potable reuse. Other parts of the world, including Singapore and Namibia, have embraced it, according to Heather Cooley, director of research at the Oakland-based Pacific Institute, a water think tank.

The impact on water supplies in California will not be immediate. Even after the water board approves the regulations, they cannot take effect until the state's Office of Administrative Law signs off, which would likely happen next summer or fall. And it could be another several years before the first projects receive approval.

Coastal communities will particularly benefit from California’s proposed rules, Cooley said. That is because they typically discharge wastewater in the oceans, not rivers, and therefore do not have to worry about whether reusing treated sewage will take water away from fragile ecosystems or downstream users. 

Plenty of water is already reused in California, but it is not immediately funneled back into taps after treatment. 

Treated wastewater is increasingly widely used for irrigation, including in the Napa Valley, and for industrial uses. 

And in a few parts of California, treated wastewater is pumped down into aquifers, where it mixes with groundwater before being pumped back up, treated again and sent to taps. That is a slower and less direct process than would be possible under the new rules the water board is considering.

A longstanding project in Orange County is the marquee example of such “indirect potable reuse” (that’s where Polhemus tasted some treated wastewater, even before it was pumped down into an aquifer). But other communities are working on similar projects. For example, Valley Water in Santa Clara County is working on a partnership with Mountain View and Palo Alto to reuse treated wastewater after it has been sent into an aquifer and has mingled with groundwater, according to assistant officer Kirsten Struve.

Large buildings in San Francisco also have requirements — potentially unique in the country, according to Cooley — to reuse some water on-site, albeit for non-potable applications such as landscaping and flushing toilets. The city has also been thinking about how it might directly reuse potable water.  Experimentation a few years ago at a San Francisco Public Utilities Commission building on Golden Gate Avenue showed that “this approach to highly treated water is viable and reliable,” John Coté, a spokesperson for the commission, said by email.

“We plan to make upgrades to our onsite water treatment system in our building for ongoing research,” Coté added, noting that the commission is doing technical analysis on several potential purified water projects, including one in San Francisco. 

A big hurdle is cost, which is significant — and probably too high for many small communities. But direct potable reuse is substantially cheaper than desalination, Polhemus said.

Acceptance among ordinary people who would drink the water remains a concern; Struve estimates that one-third of the public is not keen on the concept. However, water experts believe that Californians are increasingly receptive to direct potable reuse — in part due to water scarcity struggles statewide. 

Conscious of the public's concerns, many water agencies plan to start small. Valley Water in Santa Clara County, for example, hopes to start a pilot project for direct potable reuse before rolling it out longer term in a partnership with the city of San Jose. Currently, about 5% of Valley Water’s supplies come from recycled water (though none is currently sent to taps); the agency aims to increase that number to 10%, Struve said.

Under the new rules, direct potable reuse cannot be the only source of supply for a local water agency (though there is no real limit otherwise). That allows for some cushion just in case the water needs to be dumped.

One of the biggest issues the water board has grappled with, Polhemus said, is the risk of an unknown chemical or pathogen that is not directly monitored entering the water supply. However, because water agencies test for many things that can be similar to those unknown contaminants, the risk is considered low.

For example, Polhemus said, when the coronavirus pandemic hit, there were early worries that the novel virus would be transmissible via drinking water. But the ability of water treatment systems to handle other viruses helped establish confidence that the coronavirus too could be handled by treatment systems.

Cooley noted that direct potable reuse is an opportunity to raise the public’s awareness about what they are sending down the drain, to prevent contaminants like pharmaceuticals “from getting into wastewater systems in the first place.” 

Reach Kate Galbraith: kgalbraith@sfchronicle.com