City And County Of San Francisco County, California: drinking water report. San Francisco's 24 zip codes receive water from a system unlike most US cities.
San Francisco's 24 zip codes receive water from a system unlike most US cities. The Hetch Hetchy Reservoir in Yosemite National Park supplies roughly 85% of the city's drinking water through a 167-mile gravity-fed aqueduct, with supplemental sources from local reservoirs in Alameda and San Mateo counties. The San Francisco Public Utilities Commission manages this supply for approximately 2.7 million Bay Area residents, making it one of the largest municipal water systems in California.
San Francisco's water quality reflects both its pristine Sierra Nevada source and the aging urban infrastructure that delivers it. Hetch Hetchy water starts exceptionally pure, requiring minimal treatment compared to systems that rely on groundwater or local surface sources. The Sierra snowmelt naturally filters through granite, producing water low in minerals and contaminants. However, the system's advantage at the source doesn't eliminate concerns at the tap.
Lead remains the primary concern in San Francisco homes, particularly in neighborhoods built before 1986 when lead solder was banned. The city's hilly terrain and older housing stock in areas like the Mission, Sunset, and Richmond districts mean many buildings still have lead service lines or interior plumbing that can leach lead into drinking water. California's lead action level requirements are stricter than federal standards, but individual homes can still exceed safe levels depending on pipe age and water chemistry. The SFPUC has been replacing lead service lines, yet thousands remain throughout the city.
PFAS contamination presents a different challenge. While Hetch Hetchy water itself contains minimal PFAS due to its protected watershed, local groundwater sources used during drought years have shown detectable levels. The UCMR5 monitoring program has identified PFAS in California municipal systems at varying concentrations, and San Francisco's blend of sources means residents may experience different exposure levels depending on seasonal water sourcing. The city has invested in monitoring but, like many California utilities, faces the challenge of treating for compounds that weren't regulated when much of the infrastructure was built.
Disinfection byproducts form as chlorine (added for safety during the long journey from Hetch Hetchy) reacts with organic material in the distribution system. Total trihalomethanes and haloacetic acids typically stay within regulatory limits, but levels can vary by neighborhood based on distance from treatment facilities and water residence time in pipes. Neighborhoods at the system's edges sometimes see higher concentrations simply because water sits longer in pipes before reaching taps.
Residents in older buildings should consider testing for lead, especially if they have children or are pregnant. Those concerned about PFAS or disinfection byproducts may want to review filtration options that address multiple contaminants rather than single issues. Check your water for current data on your specific zip code, review the water filter guide for certified options that match San Francisco's contamination profile, request your detailed report for building-specific insights, or visit the California state page for broader context on state water quality patterns.