Sunnyvale Water Hardness & Quality Report (2026)

Sunnyvale is served by the City of Sunnyvale Water Utility, which operates a mixed supply system. The northern portion of the city receives treated surface water from the San Francisco Public Utilities Commission (SFPUC), sourced from reservoirs in the Sierra Nevada, Alameda County, and San Mateo County. The southern portion receives treated surface water from Santa Clara Valley Water District (Valley Water), imported via the South Bay Aqueduct, Dyer Reservoir, Lake Del Valle, and San Luis Reservoir — all drawing from the Sacramento–San Joaquin Delta watershed — with Calero Reservoir as a local source. The city supplements these supplies with local groundwater from deep aquifers in northern San Mateo County, treated at three Valley Water plants in Santa Clara County.

Sunnyvale's water crosses multiple watersheds and geological zones. SFPUC surface water originates in the Sierra Nevada and coastal ranges, while groundwater is stored in deep aquifers beneath the San Francisco Bay Area. Santa Clara County's groundwater naturally contains elevated mineral concentrations, averaging over 250 mg/L hardness due to mineral-rich geological formations. The blended supply — combining Sierra Nevada snowmelt, Sacramento–San Joaquin Delta imports, and local groundwater — results in a hard character typical of the region, with the SFPUC-supplied portion maintaining filtered turbidity at or below 0.3 NTU at least 95% of the time.

At the hard hardness level, scale buildup in water heaters, kettles, and dishwashers is common and accelerates over time. Soap and detergent efficiency is reduced, requiring higher doses for effective cleaning. Appliances with heating elements — washing machines and coffee makers — experience shortened lifespans from mineral deposits, and hard water leaves spots on glassware and reduces lather in showers. A water softener is recommended for households seeking to reduce scale formation and extend appliance longevity, though softening adds sodium to the supply. pH, lead/copper, and PFAS data are available through the city's annual Consumer Confidence Report and Valley Water's published water quality documentation, confirming compliance with Safe Drinking Water Act requirements.