Pasadena Water Hardness & Quality Report (2026)

Pasadena Water and Power (PWP) serves approximately 138,000 residents across a 40-square-mile area in Pasadena, Los Angeles County, California. The utility blends imported surface water from the Metropolitan Water District (MWD) — primarily the Colorado River via the Colorado River Aqueduct and the State Water Project from Northern California — with local groundwater from the Raymond Basin aquifer. PWP operates seven wells tapping the Raymond Basin at 300–500 feet depth, producing an average of 13 million gallons daily (about 40% of supply). Treatment includes filtration, disinfection with chloramine, and fluoridation at the Pasadena Water Treatment Plant and wellhead facilities.

The Raymond Basin aquifer is recharged by precipitation percolating from the San Gabriel Mountains into unconsolidated alluvial gravels and sands overlying Pliocene-Pleistocene sedimentary deposits, including the Fernando Formation, which is rich in limestone and dolomite. Imported water traverses the Colorado River watershed, interacting with arid basin limestones and evaporite formations from Mesozoic and Cenozoic sedimentary layers, as well as the State Water Project's Sierra Nevada snowmelt. This dual sourcing from carbonate-influenced groundwater and mineral-laden imported surface water imparts a hard character through natural dissolution of calcium and magnesium.

Very hard water promotes significant scale buildup in pipes, reducing water heater efficiency by up to 29% and shortening lifespan from 12–15 years to 6–8 years. Affected appliances include water heaters, washing machines (requiring 35% more detergent), dishwashers (causing spots on glassware), and faucets with visible deposits. Recommended maintenance includes installing scale-inhibiting filters, flushing water heaters biannually, and using vinegar soaks for fixtures. A whole-home water softener is strongly recommended to mitigate damage and extend appliance life. Pasadena's water meets Safe Drinking Water Act standards with pH typically 7.5–8.5; reports note contaminants including hexavalent chromium and arsenic from natural geology, all below legal limits. Annual Consumer Confidence Reports from PWP provide full testing results.