San Francisco Bay Area CA metro: water quality. The Bay Area's water supply is a study in contrasts.
The Bay Area's water supply is a study in contrasts. San Francisco itself draws almost entirely from the Hetch Hetchy Reservoir in Yosemite National Park – snowmelt carried 167 miles through gravity-fed aqueducts, consistently ranked among the cleanest municipal supplies in the country. Cross the Bay Bridge to Oakland, and the East Bay Municipal Utility District (EBMUD) sources from the Mokelumne River. Head south to San Jose, and Santa Clara Valley Water District blends imported water from the Sacramento-San Joaquin Delta with local groundwater and recycled supplies. Fremont falls under the Alameda County Water District, with yet another mix.
Nine counties, dozens of water agencies, 7.75 million people – and no two cities in this metro drink the same water.
PFAS monitoring under UCMR5 has revealed a split picture across the Bay Area. San Francisco's Hetch Hetchy supply has shown minimal PFAS detections, which tracks with its remote mountain watershed origin. Groundwater-dependent systems in the South Bay and East Bay tell a different story. Santa Clara County, home to decades of semiconductor manufacturing and aerospace work, has documented PFAS contamination in several groundwater basins.
The California State Water Resources Control Board established notification levels of 5.1 ppt for PFOA and 6.5 ppt for PFOS – among the strictest triggers in the nation. Response levels that force utility action are set at 10 ppt and 40 ppt respectively. Moffett Federal Airfield in Mountain View, a former Naval Air Station, is a confirmed PFAS source. The EPA designated it a Superfund site, and groundwater remediation has been ongoing since the 1980s for solvents, with PFAS added to the cleanup scope more recently.
Our data brings together state notification-level exceedances, UCMR5 results, and individual district reports so you can compare what your specific water agency has found versus what neighboring systems report.
Within California, the Bay Area generally fares better than Southern California metros that rely heavily on Colorado River water and contaminated groundwater basins. The region's access to high-quality Sierra Nevada surface water gives San Francisco and parts of the East Bay an advantage that most American cities lack.
But the South Bay groundwater situation is a counterweight. A 2023 investigation by San Jose Spotlight found PFAS detections in multiple South Bay wells, some linked to industrial activity dating back to the 1960s. According to the Regional Water Quality Control Board, at least 23 sites in Santa Clara County are under investigation or cleanup for PFAS contamination.
See our California state page for broader context.
Where you live in the Bay Area determines your water profile more than almost any other metro in the country. A renter in the Sunset District of San Francisco is drinking Hetch Hetchy snowmelt. A homeowner in south San Jose may be getting groundwater blended with Delta imports.
Check your water to find out which agency serves you and what they've reported. If you're in the South Bay or near former military or industrial sites, a reverse osmosis or activated carbon system is worth considering – see our water filter guide for tested options. Our detailed report can show you multi-year trends for your area, which is especially useful if you're near a Superfund site where contamination levels are actively changing.