Beyond Hetch Hetchy – Understanding San Francisco’s Water System

Many people may be familiar with Hetch Hetchy, San Francisco’s major water source that lies within Yosemite National Park. The water at Hetch Hetchy contains spring snowmelt flowing down the Tuolumne River. What many people may not know is that this same water is a protected primary source exempt from filtration requirements by the U.S. Environmental Protection Agency and the State Water Resources Control Board’s Division of Drinking Water.  

Hetch Hetchy; dome and Kolana rock in snow.
Hetch Hetchy Reservoir.

The SFPUC’s Hetch Hetchy Regional Water System is comprised of several reservoirs that span the 168-mile distance between San Francisco and Yosemite. Surface water from local watersheds, upcountry sources, and local groundwater all contribute to the water that comes out of the faucet. Rainfall and runoff from the 35,000-acre Alameda Watershed in Alameda and Santa Clara counties are collected in Calaveras Reservoir and San Antonio Reservoir. This water is delivered to the Sunol Valley Water Treatment Plant. Subsequently, rainfall and runoff from the 23,000-acre Peninsula Watershed in San Mateo county is stored in the Crystal Springs, San Antonio, and Pilarcitos reservoirs, and this water is delivered to the Harry Tracy Water Treatment Plant.

Peninsula Watershed
Calaveras Reservoir.

In 2018, a small amount of groundwater from four San Francisco wells was intermittently added to these surface water supplies. The use of this local groundwater supply helps to expand the SFPUC’s total water sources and increases the reliability of drinking water delivery in the City.

It is easy to see how the Hetch Hetchy Regional Water System as a whole is much more than the sum of its parts. Although Hetch Hetchy is integral to delivering tap water to San Francisco and beyond, it is the wider system as a whole that works to make it possible for the SFPUC’s customers to have reliable tap water every day.