Simi Valley Water Hardness & Quality Report (2026)

Golden State Water Company (GSWC) serves Simi Valley, drawing water from the State Water Project — imported from Northern California via the Metropolitan Water District — and supplemented by groundwater from the Gillibrand Groundwater Basin north of the city. The primary treatment facility is the Joseph Jensen Filtration Plant in Granada Hills, operated by the Metropolitan Water District. Secondary sources include the Lake Bard Water Filtration Facility (emergency reserve), the Metropolitan Weymouth Plant in La Verne, and the Calleguas Wellfield west of Moorpark. Groundwater from the Gillibrand Basin is treated at the Tapo Canyon Water Treatment Plant before distribution.

The Gillibrand Groundwater Basin lies within Southern California's Transverse Ranges, where mineral-rich geological formations dissolve calcium and magnesium carbonates into groundwater, producing naturally hard conditions. This groundwater component comprises approximately 18.3% of the total supply, with the remaining 81.7% sourced from the State Water Project. The State Water Project surface water travels from Northern California and carries lower mineral content; blending with the harder local groundwater results in the overall hard supply characteristic of the Transverse Ranges region, where formations rich in dissolved mineral salts are common.

GSWC blends treated surface water (81.7%) with groundwater (18.3%) to meet all EPA Maximum Contaminant Levels (MCLs). Simi Valley's hard water causes noticeable scale buildup on fixtures and appliances, reduces soap lathering, and can cause dry skin. Water heaters, dishwashers, and washing machines are most affected by mineral accumulation, and homeowners should expect increased maintenance requirements. Regular descaling of fixtures prevents clogging and efficiency loss, and a water softener is recommended to extend appliance lifespan and reduce energy consumption. Perchlorate levels have never exceeded the California state standard of 6.0 µg/L, and the Consumer Confidence Report (CCR) is available at www.gswater.com/simi-valley.