Water Hardness in San Diego

San Diego's tap water is very hard, averaging roughly 219 mg/L of calcium carbonate. The City of San Diego's annual drinking water quality reporting has put total hardness across its three treatment plants — Alvarado, Miramar and Otay — in the region of 216 to 230 ppm, around 13 grains per gallon, with the city advising customers that some areas and demand conditions push higher still.

The explanation is that San Diego grows very little of its own water. The large majority is imported: Colorado River water delivered via the San Diego County Water Authority, and State Water Project deliveries originating in Northern California. Colorado River water is the harder of the two by a wide margin, having travelled hundreds of miles through limestone, gypsum and evaporite deposits across the Southwest, accumulating dissolved calcium, magnesium and sulfates. State Water Project water is more moderate. The Claude "Bud" Lewis desalination plant in Carlsbad adds a further, locally produced component to the regional supply.

Because the ratio between these sources shifts with allocation, drought status and demand, San Diego hardness moves around more than a single average suggests — the difference between the city's reported plant averages and the higher figures it advises customers to expect reflects that variability rather than a contradiction.

Practically, 219 mg/L means scale is a persistent maintenance item rather than an occasional one. Shower doors spot and etch, fixtures develop deposits within weeks to months, and water heaters lose efficiency without periodic flushing. San Diego's substantial share of older housing stock compounds this where plumbing has already narrowed. As elsewhere in California, check local rules before installing a salt-based softener: brine discharge restrictions apply in parts of the state, and salt-free scale inhibition is a common alternative.