Mission District Water Hardness & Quality Report (2026)

The Mission District in San Francisco is served by the San Francisco Public Utilities Commission (SFPUC), delivering water to over 800,000 residents across the city and parts of San Mateo County. The primary supply is the Hetch Hetchy Regional Water System, sourcing from the Tuolumne River via reservoirs including Hetch Hetchy, Cherry Lake, and Lake Eleanor. Local groundwater from the Westside Aquifer and blending at facilities such as Sunset Reservoir and Crystal Springs Reservoir support distribution. Treatment occurs at the O'Shaughnessy and Sunol facilities, involving filtration, chloramine disinfection, and fluoridation.

Water flows from the Tuolumne River watershed in Yosemite National Park, spanning granitic Sierra Nevada geology of the Mesozoic Sierra Batholith, including granodiorite and tonalite — igneous rocks that contribute minimal dissolved calcium and magnesium, yielding a soft source. Sedimentary rocks of the Franciscan Complex, comprising Jurassic-Cretaceous sandstone, shale, and chert, underlie local groundwater in the Westside Groundwater Aquifer, releasing more ions through weathering. This mixed sourcing from igneous and sedimentary formations creates a moderately mineralised profile overall.

Limescale buildup in pipes, water heaters, dishwashers, and coffee makers reduces efficiency and lifespan; washing machines and boilers may require more detergent. Regular vinegar descaling and using low-flow fixtures help mitigate effects. A water softener is often recommended for households with frequent scaling issues, though added sodium may be a concern for those on low-sodium diets. SFPUC water maintains pH around 8 (range 7.7–8.4), with no notable PFAS detections; all federal and state standards are met, with treatment including ozonation, filtration, UV disinfection, and chloramination.