Claremont Water Hardness & Quality Report (2026)

Golden State Water Company (GSWC) operates the Claremont Water System, serving the City of Claremont in Los Angeles County, California, with a population of around 37,000. The utility sources water from local groundwater via the Pomona Valley basin, imported surface water from the Metropolitan Water District through Three Valleys Municipal Water District, and minimal additional surface supplies. Treatment occurs at blending facilities with chloramination for disinfection; aggressive monitoring covers 37 systems across the service area in this foothill community near the San Gabriel Mountains.

The watershed encompasses the upper Santa Ana River drainage, with recharge from San Gabriel Mountain snowmelt and rain filtering into the Pomona Valley groundwater basin. Key geology includes alluvial aquifers in Quaternary sediments over Miocene Fernando Formation sandstones and shales, with limestone lenses and evaporitic influences. These formations yield a hard supply as water percolates through mineral-rich layers picking up dissolved calcium and magnesium cations. Imported portions from distant reservoirs dilute but do not fully offset the basin's mineralized character, managed under Six Basins Watermaster adjudication.

Very hard water in Claremont promotes significant limescale buildup in pipes, heaters, and fixtures, reducing efficiency in water heaters, dishwashers, and washing machines by up to 50% over time. Coffee makers and kettles require frequent descaling; faucet aerators show white deposits and spotted dishes are common. Maintenance involves vinegar soaks, annual heater flushes, and low-flow showerheads. A water softener is highly recommended to extend appliance life and improve soap efficiency. Recent CCRs confirm EPA compliance with pH stable at 7.5–8.5; seven contaminants exceed health guidelines including arsenic and hexavalent chromium from natural geology.