Since the early 1930s, San Francisco’s drinking water has flowed from the Hetch Hetchy Valley of northwestern Yosemite, funneling through a myriad of pipes along 167 miles, before landing in city reservoirs and out its taps. Its pristine nature has long been a source of bragging rights for San Francisco’s Public Utilities Commission, which even bottles and sells Hetch Hetchy water. But, starting in 2017, a small percentage of the city’s drinking water will come from its own backyard as San Francisco taps into its groundwater to help quench its thirst.
“San Francisco hasn’t used groundwater for drinking since the 1930s,” said Jeff Gilman, the SFPUC’s groundwater project manager.
In an effort to diversify its water supply, the city is digging a series of six wells between Golden Gate Park and San Bruno to tap into the underground aquifer. A small amount of the water will be blended with the Hetch Hetchy drinking water, destined for customer delivery.
The groundwater will make-up a minuscule percentage of San Francisco’s water use — contributing about 4 million gallons a day to the 65 million gallons the city uses daily. Although the project was set in motion before California’s drought fully kicked in, officials said the groundwater project would provide the city an alternative source of water in the event of future droughts and disasters.
“So that gives us some added insurance in the event of some major catastrophe where pipelines are disrupted,” Gilman said. “We can count on a local source of drinking water.”
The groundwater isn’t as sparklingly clean as the snowmelt water flowing out of Yosemite. The SFPUC said tests on the groundwater revealed nitrate levels higher than state standards. But officials said treating it with chlorine and blending a small percentage with Hetch Hetchy water will dilute it to safe levels. And officials said recent taste tests show the water’s flavor won’t be noticeably altered.
“Our customers won’t even discern a difference in the taste or the quality of the water,” said Katie Miller, manager of the SFPUC’s distribution system.
The city recently temporarily drained one of the twin tanks at Sunset Reservoir in the city's Sunset District for cleaning and to install a large pipe that will feed the newly-tapped groundwater into the massive tanks when the system goes operational in 2017.
“We can bring in very high quality groundwater from 300 feet below San Francisco,” Miller said, “and blend it with the water here at Sunset Reservoir.”
Beneath the glow of massive spotlights, crews hosed and scraped at layers of silt from the floor of one of the reservoir's tanks. Normally, San Francisco fire crews would help keep the tanks clean by flushing water lines at above ground hydrants — but because of the drought the city has curtailed such cleanings. The pair of tanks has the capacity to hold 177 million gallons of water in underground vaults stretching eight city blocks.
“It’s kind of a little bit eerie because it’s so vast,” Gilman said, stepping through the darkened, cavernous room where the echoes of the cleaning created an atmospheric din.
San Francisco relied on groundwater until the Hetch Hetchy system opened in 1934 — following the controversial damming of the Hetch Hetchy Valley. Since then, the city has only used groundwater to irrigate Golden Gate Park and the San Francisco Zoo. But very soon that same water will make the short journey to homes and businesses across the city — for the first time in nearly nine decades.