San Francisco Water Hardness & Quality Report (2026)

The San Francisco Public Utilities Commission (SFPUC) delivers water to approximately 2.7 million customers across San Francisco and parts of San Mateo, Alameda, and Santa Clara counties. The primary source is Hetch Hetchy Reservoir on the Tuolumne River, supplemented by local reservoirs including Crystal Springs, San Andreas, and Calaveras in the Peninsula and Alameda watersheds, plus minor groundwater from wells. Water is conveyed via the Hetch Hetchy Aqueduct system, a 167-mile gravity-fed network of dams, tunnels, pipelines, and pump stations. Treatment occurs at the Sunol Valley Water Treatment Plant and O'Brien Water Treatment Plant, focusing on disinfection and filtration as needed.

The Hetch Hetchy watershed spans protected federal lands in the Sierra Nevada, underlain by the Sierra Nevada batholith — primarily Mesozoic granodiorite and metavolcanic rocks with virtually no limestone or dolomite. Rapid snowmelt runoff at high elevation minimizes contact time with mineral-bearing soils, preventing significant dissolution of calcium and magnesium. Local Peninsula reservoirs draw from similar coastal range geology, reinforcing the soft character without significant mineralization from deeper carbonate formations.

Soft water at 32 mg/L means minimal limescale buildup on kettles, coffee makers, and dishwashers, with reduced maintenance needs. Soap lathers efficiently and skin and hair feel less dry compared to harder supplies. No water softener is recommended, as it would unnecessarily add sodium; instead, monitor older plumbing for corrosion, which soft water can sometimes accelerate, and flush taps periodically. SFPUC water meets all federal and state standards per the 2022 CCR, with pH typically 8–9 for corrosion control; treatment includes ozonation, UV disinfection, and chloramination.