San Rafael Water Hardness & Quality Report (2026)

The Marin Municipal Water District (MMWD) provides water to San Rafael, California, serving much of Marin County and over 190,000 residents across 150 square miles. Primary sources are seven reservoirs — Nicasio, Soulajule, Stafford, Phoenix, Bon Tempe, Alpine, and Kent Lakes — located in protected watersheds around Mt. Tamalpais. Supplemental supply comes from the Sonoma County Water Agency via the North Marin Water Project. Treatment occurs at the San Rafael Treatment Plant and the Harvey Cove Filtration Plant before distribution throughout the service area.

The Mt. Tamalpais watersheds encompass granitic intrusions and the Franciscan Complex, a Mesozoic accretionary mélange of sandstone, shale, chert, and greenstone with sparse limestone. Runoff from these protected forested uplands into reservoirs produces very soft water due to low weathering of calcium and magnesium-bearing rocks. The absence of significant limestone development minimizes mineral dissolution, maintaining a low-mineral profile distinct from harder groundwater drawn from karst aquifers.

With soft water, scale buildup is negligible, preserving water pressure and extending appliance life — dishwashers, washing machines, and water heaters face minimal mineral deposits, reducing energy costs and maintenance. Soap lathers efficiently, requiring less detergent and avoiding scum. No water softener is needed; instead, monitor for corrosion risks in soft water systems and use corrosion inhibitors if necessary. MMWD conducts over 115,000 tests annually; pH typically ranges 8.0–9.0 due to lime stabilization, with no notable PFAS detections and lead action levels not exceeded in recent Consumer Confidence Reports; treatment includes ozonation, filtration, and chloramination.