Union City Water Hardness & Quality Report (2026)

Union City, California receives its drinking water from the Alameda County Water District (ACWD), serving Fremont, Newark, and Union City in Alameda County. ACWD sources water from a mix of local groundwater from the Niles Cone Groundwater Basin and treated surface water imported from the State Water Project via the South Bay Aqueduct. Primary treatment occurs at the Newark Treatment Plant, with the Zone 7 Water Agency also contributing groundwater resources, ensuring reliable delivery to over 380,000 residents across the district.

The watershed encompasses the Sacramento-San Joaquin Delta and local East Bay groundwater basins, with recharge from distant Sierra Nevada snowmelt funneled through the Delta-Mendota Canal. Geologically, the supply interacts with Quaternary alluvium and Tertiary sediments of the Santa Clara Valley, overlying Franciscan melange rocks that impart a mineralised character through natural dissolution of calcium and magnesium from volcanic and metamorphic bedrock. This results in moderately mineralised water, shaped by sandy-gravel aquifers that allow moderate mineral pickup without extreme concentrations seen in harder inland regions.

At moderately hard levels, scale buildup occurs noticeably in dishwashers, washing machines, and water heaters, reducing efficiency and lifespan by 20–30% without mitigation. Coffee makers and kettles show spotting, while bathroom fixtures develop films over time. Regular vinegar descaling, low-flow aerators, and magnetic descalers help; a water softener is recommended for households with hard water concerns. ACWD water meets all EPA standards with no MCL violations; pH typically ranges 8.5–9.5 for corrosion control, with lead and copper compliance achieved via orthophosphate addition and no PFAS exceedances noted in recent tests.