San Lorenzo Water Hardness & Quality Report (2026)

San Lorenzo, California, in Alameda County between San Leandro and Hayward along the San Francisco Bay shoreline — a planned post-World War II suburban community developed in the late 1940s with characteristic ranch-style homes on the East Bay flatlands — receives its municipal water from East Bay Municipal Utility District (EBMUD), drawing from the Mokelumne River in the central Sierra Nevada. EBMUD conveys Sierra Nevada snowmelt and rainfall 100 miles via aqueducts to Pardee Reservoir in Amador County, treats it, and distributes throughout the East Bay service area.

The very soft 32 mg/L hardness and very low TDS of 65.1 mg/L are characteristic of EBMUD's Mokelumne River supply at its most pristine. The Mokelumne River originates in the Amador and Calaveras counties Sierra Nevada — draining the Cretaceous Sierra Nevada Batholith (granodiorite, tonalite, quartz diorite) and associated Paleozoic and Mesozoic metamorphic rocks (Amador Group, Calaveras Complex) — crystalline terrains with essentially no soluble carbonate minerals. EBMUD has protected the Mokelumne watershed extensively, maintaining water quality standards that produce San Lorenzo's characteristically clean, soft supply.

At 32 mg/L, San Lorenzo enjoys very soft water — among the softest in the Bay Area. Soap lathers abundantly with minimal product needed, appliances scale very slowly, and glassware from the dishwasher is spotless without rinse aid. Annual descaling of kettles and coffee machines is typically sufficient. The characteristic consideration for very soft water is its mild corrosive potential — very low TDS water at 65.1 mg/L has limited mineral buffering. Older homes with lead-solder copper plumbing should flush cold taps before morning drinking. The low PFAS level of 2.9 ppt reflects EBMUD's Sierra Nevada source protection — San Lorenzo is one of the cleaner PFAS profiles in the East Bay dataset.