Explainer: Here’s How Your Water Gets From the Sierras to the City
Turn on the tap, and it’s hard to imagine your water coming all the way from the Sierra Nevada mountains.
By the time it arrives in your shower, the water likely traveled hundreds of miles over dams into reservoirs and through pipelines, with millions of gallons siphoned off to various Bay Area cities. At the end of the road is San Francisco and your faucet.
San Franciscans only use about a third of the water its water agency, the San Francisco Public Utilities Commission, owns. The other two-thirds go to cities and water agencies across the Bay Area. That’s created a dynamic in which San Francisco controls one of the most valuable assets in the region—a critical water resource as the state faces worsening drought conditions.
So here’s how it all works:
Eighty-five percent of San Francisco’s water comes from the Tuolumne River.
The other 15% comes from local creeks in Alameda County and on the Peninsula.
The water that comes from Hetch Hetchy flows down from the Sierras using only gravity, with no pump stations needed.
On its way down from the mountains, the water runs through three hydroelectric facilities, generating around 20% of the city’s electricity.
Because Hetch Hetchy is mostly snowmelt flowing into a granite basin, the water doesn’t need to be filtered, only treated.
As it makes its way down through the Bay Area, two-thirds of the water is sold and piped to the SFPUC's wholesale customers, which include local cities and regional water districts.
Once in the city, the water is piped and stored through an elaborate network of pumps, tanks, wells and reservoirs—with most ending up in homes.
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