Norwalk Water Hardness & Quality Report (2026)

Norwalk, California, in southeastern Los Angeles County, receives its municipal water supply through the City of Norwalk and the Norwalk–La Mirada Municipal Water District, sourcing from the Central Basin groundwater pumped from the Los Angeles Coastal Plain alluvial aquifer in Los Angeles County, and imported treated water from the Metropolitan Water District of Southern California (MWD) — including State Water Project and Colorado River water deliveries. The Central Basin Watermaster manages groundwater rights in the basin. Water hardness in Norwalk measures 113 mg/L — classified as moderately hard.

Norwalk's moderate hardness reflects the Central Basin groundwater character in the southeastern Los Angeles coastal plain. The Central Basin alluvial aquifer in the Norwalk area is recharged primarily by the San Gabriel River spreading grounds — where the San Gabriel River, draining the San Gabriel Mountains granodiorite and gneiss (calcium-poor crystalline rock), percolates into the gravel-filled coastal plain basin. However, the southeastern LA coastal plain shows somewhat more mineral-rich groundwater than the western zones, as the aquifer in this area has deeper alluvial deposits with longer residence times and greater contact with the more calcareous Puente Hills formation and coastal plain Quaternary sediments in the southeast basin margin.

At 113 mg/L, Norwalk residents encounter moderate scale accumulation. Faucet aerators and showerheads develop deposits after several months — monthly cleaning with citric acid solution is standard maintenance. Dishwashers produce cleaner glassware with rinse-aid. City of Norwalk Public Works and Norwalk–La Mirada MWD consistently deliver water meeting all California SWRCB and EPA Safe Drinking Water Act requirements.