SAN FRANCISCO (AP) — San Francisco’s pristine tap water from mountain runoff in the Sierra Nevada soon may be a little less pure.
City officials plan to mix groundwater into the supply starting in 2015 or 2016 in an effort to diversify and increase water reserves during California’s ongoing drought, the San Francisco Chronicle reported Monday.
San Francisco’s water comes mostly from Sierra Nevada runoff stored in the Hetch Hetchy Reservoir in Yosemite National Park. It is a source of great pride in the city and often a preferred choice over bottled water.
In contrast, the groundwater the city plans to use was found to contain nitrates, which can make people sick in high doses. But city officials say the nitrates will be diluted to safe levels when the water is mixed with Sierra runoff.
“We don’t think people will notice a difference with what they are drinking,” said Jeff Gilman, groundwater project manager at San Francisco Water Power Sewer. “It tastes the same. Color is the same. Odor is the same.”
The groundwater will be treated with chlorine in addition to being diluted with runoff at doses of between 10 and 15 percent.
Experts say drawing groundwater, which is expected to cost $66 million, is a good way to ensure the city has water in case an earthquake severs its ties to Hetch Hetchy Reservoir or climate change reduces the Sierra Nevada snowmelt.
“The city is thinking ahead. ... Having this other local water supply is a really good thing,” said David Sedlak, an environmental engineering professor at the University of California, Berkeley.
About 80 percent of California residents rely on some amount of groundwater, Sedlak said.
The roughly 45-mile basin San Francisco will draw from for its groundwater was the city’s main water supply before the pipeline to Yosemite was completed in 1934, the Chronicle reported. Other nearby cities that receive Hetch Hetchy water already tap it for groundwater.
Agreements have been drafted to ensure the basin is not overdrawn, according to the newspaper.