San Diego Water Hardness & Quality Report (2026)

City of San Diego Public Utilities Department serves the city and surrounding areas from three primary sources: the Colorado River Aqueduct, the State Water Project (connected to the Sacramento–San Joaquin River Delta), and local reservoir storage. Water is treated at multiple facilities, including the Robert A. Skinner Treatment Plant in Riverside County (capacity 350 million gallons per day) and the San Marcos Submerged Membrane Treatment Plant, which serves up to 220,000 households annually. San Diego imports approximately 90% of its water from outside sources due to limited local supplies.

The Colorado River drains Paleozoic limestone and dolomite formations and Mesozoic sandstones and shales across the Colorado Plateau, accumulating dissolved minerals over thousands of miles of transport. The State Water Project draws from the Sacramento–San Joaquin Delta, where Cenozoic alluvial deposits and marine sediments contribute additional dissolved calcium and magnesium. These geological characteristics produce a naturally very hard supply averaging 16 grains per gallon (276 ppm).

At 276 ppm, very hard water causes mineral deposits on dishes and fixtures, reduces soap and shampoo lathering, and drives scale buildup in water heaters and appliances that can shorten their lifespan. A water softener is strongly recommended, particularly in older homes with legacy plumbing. The San Diego County Water Authority monitors water quality continuously; the Environmental Working Group has identified eight carcinogenic contaminants above health guidelines—including TTHMs (trihalomethanes), HAAs (haloacetic acids), and chromium-6—though all remain below EPA legal limits. Active carbon filtration is recommended for additional contaminant reduction.