Patterson Water Hardness & Quality Report (2026)

Patterson, California, in Stanislaus County — a Central Valley city in the Diablo Range foothills corridor between Modesto and Tracy, historically celebrated as the Apricot Capital of the World and now a major logistics hub at the I-5/Route 33 interchange — receives its municipal water from the City of Patterson Water Utility, which draws from the Delta-Mendota Canal (DMC) State Water Project import supply and local San Joaquin Valley alluvial groundwater through a blended treatment system. Patterson is in the San Joaquin Valley's western trough, where water supply depends on both SWP import and local valley aquifer production.

The moderately hard 169.5 mg/L hardness and elevated TDS of 513.3 mg/L reflect the western San Joaquin Valley supply's complex geological character. The Delta-Mendota Canal supply delivers Sacramento-San Joaquin Delta water (a blend of Sierra Nevada soft water and Central Valley agricultural return flows), already moderately mineralized from Delta transit. Local Patterson alluvial groundwater in the western San Joaquin Valley trough draws from Quaternary and Pliocene alluvial fan deposits derived from the Coast Range — the Diablo and Inner Coast Range marine sedimentary terrain (Cretaceous and Eocene shale, sandstone, and minor limestone) — and from the Central Valley floor's accumulation of evaporite minerals concentrated by decades of agricultural irrigation and evaporation. This blended supply produces harder, higher-TDS water than typical Sierra Nevada-dominated supplies.

At 169.5 mg/L, Patterson's water is moderately hard — consistent with western San Joaquin Valley supply profiles. Scale builds in kettles and appliances over months, dishwashers benefit from rinse aid, and faucet aerators need periodic cleaning. Quarterly descaling of heating appliances is the standard schedule. The PFAS level of 6.9 ppt warrants a certified drinking water filter — the San Joaquin Valley agricultural corridor's PFAS pesticide applications, the Tracy area logistics warehousing and military depot legacy, and the Central Valley's concentrated agricultural and industrial PFAS background contribute to Patterson's supply profile.