From toilets to taps: SF tests new water recycling program

By Dominic Fracassa, San Francisco Chronicle, November 20, 2019

Manisha Kothari looked every bit the bartender as she filled a dozen shot glasses, pouring carefully from a slender pitcher.

But what Kothari served on a weekday morning at the San Francisco Public Utilities Commission’s headquarters was not a round of spirits.

It was the culmination of more than a year’s worth of research into how San Francisco might someday tap a new source of potable water, turning what’s now a waste product into clear, cool drinking water. What Kothari, a water resource specialist, filled the glasses with looked, smelled and tasted like what comes out of any city faucet, but it had been harvested from the San Francisco water agency’s toilets, sinks and shower drains.

As cities across California and throughout the world confront the climate change crisis and the worsening droughts expected to follow, they are considering using purified wastewater to supplement their existing drinking water. San Francisco’s wastewater recycling efforts are nascent, Kothari said.

It will be years before purified wastewater can be added to the city’s existing supplies, which mostly comes from the Hetch Hetchy Reservoir. There are no firm timelines, but over the next few years, the agency will test its purification system, sharing much of the data it collects with state regulators, Kothari said. State legislation establishing the rules for turning wastewater into drinking water is expected to be introduced in 2023. But even then, the agency expects to conduct a lengthy public information campaign, educating residents about the process and fielding safety concerns.

The city is also sharing data and best practices with other California cities and with state regulators as the process gains traction and acceptance. Orange County has been in the vanguard of water recycling efforts for decades. The water agency there injects purified wastewater back into the groundwater, where it mingles with existing supplies.

“So if you go to Disneyland, you’re already getting some of that,” said Kothari, who’s managing the commission’s wastewater purification research program, dubbed PureWaterSF.

The purification technology San Francisco is using is broadly similar to Orange County’s, Kothari said. But unlike Orange County, San Francisco has no location to store treated wastewater.

In the future, wastewater purification likely would be done at the municipal, rather that the individual-building level, Kothari said, for reasons of scale and so the city could ensure rigorous water-quality standards are met. The commission’s headquarters represents a convenient testing ground for the filtration process, however.

“As we prepare for things like climate change, we have to look at ways to diversify our water supply,” said commission General Manager Harlan Kelly. “Our main source of water is 167 miles away and crosses three fault lines. As technology evolves, projects like this become scalable, and this is a part of the wave of the future.”

The commission has been capturing, treating and reusing wastewater to flush the toilets at its headquarters since the Golden Gate Avenue building opened in 2012. For its potable water research, the agency takes roughly 4,000 gallons from that supply and subjects it to a three-step purification process.

First, the wastewater goes through a process that filters out suspended solids and bacteria. Next, the water undergoes reverse osmosis that removes viruses and dissolved solids, like salts. Finally, the water passes through a disinfectant ultraviolet light that destroys any trace chemical pollutants.

The estimated 1,600 gallons that go through the purification process each day is carefully assessed, and in most cases, the water is returned to the agency's non-potable supply, used to flush the building’s toilets.

The water is cleaned to such an extent, Kothari said, that compounds like chloramine — a combination of chlorine and ammonia commonly used to treat drinking water — have to be blended back in to resemble the taste of ordinary tap water.

And while any regular reliance on recycled wastewater is still many years away for San Francisco, it still raises a basic question: Can residents stomach the idea of drinking water that once circled a toilet bowl? Many in the city blanched in 2017 when the commission began adding groundwater into the supply flowing from Hetch Hetchy. But with enough education, outreach and assurances of the water’s safety, residents will come around, said Paula Kehoe, the commission’s director of water resources.

“We understand that it’s potentially a different type of water source than people are traditionally used to,” she said. “We need to ensure that it’s safe. We need to open up our books and show the data and encourage the community to ask us questions. ... This is a partnership with the community.”


Dominic Fracassa is a San Francisco Chronicle staff writer. Email: dfracassa@sfchronicle.com Twitter: @dominicfracassa

 

Sitemap: