Pasadena Water Hardness & Quality Report (2026)

Pasadena, California receives its municipal water supply through the City of Pasadena Water and Power (PWP), drawing from three distinct sources: local groundwater from the Raymond Basin — the principal alluvial aquifer beneath the western San Gabriel Valley in Los Angeles County; imported water from the Los Angeles Department of Water and Power (LADWP) Owens Valley and Mono Basin aqueduct system (Sierra Nevada snowmelt); and imported water from the Metropolitan Water District of Southern California (MWD) carrying both Colorado River and State Water Project water. Water hardness in Pasadena reaches 165.5 mg/L — classified as hard, elevated by the significant Colorado River MWD fraction and mineralised Raymond Basin groundwater.

Pasadena's hard supply reflects the combined mineral loading of its multiple sources. The Raymond Basin groundwater is recharged by the San Gabriel River and its tributaries descending from the San Gabriel Mountains — Precambrian gneiss, Mesozoic granodiorite, and Cretaceous intrusive complexes that contribute moderate dissolved calcium during long aquifer residence times. MWD Colorado River water carries substantial mineral loads from Permian Kaibab Limestone and Triassic carbonate canyon geology of the Colorado Plateau. Even the LADWP Owens Valley aqueduct water, while inherently soft, blends with these harder sources to produce the finished hardness. The Raymond Basin fraction — the most mineralised component — pulls the blended supply into the hard category.

At 165.5 mg/L, Pasadena residents face regular limescale challenges. White calcium deposits accumulate on faucet aerators, showerheads, and tile surfaces within weeks — monthly descaling with citric acid or vinegar solution is standard maintenance. Dishwashers produce consistently better results with rinse-aid, and water heaters benefit from annual element inspection. Pasadena Water and Power consistently delivers water meeting all California SWRCB and EPA Safe Drinking Water Act requirements throughout its Pasadena service area.