Downey Water Hardness & Quality Report (2026)

Downey, California, in southeastern Los Angeles County, draws its municipal water supply through the City of Downey Public Works Department and the Central Basin Municipal Water District (CBMWD), sourcing from two primary origins: local Central Basin groundwater pumped from the Los Angeles Coastal Plain alluvial aquifer in Los Angeles County; and imported treated water from CBMWD via the Metropolitan Water District of Southern California (MWD) — including State Water Project and Colorado River water. The Central Basin is the main production aquifer for southeastern Los Angeles County communities. Water hardness measures 75.5 mg/L — classified as moderately soft.

Downey's moderately soft supply reflects the Central Basin groundwater character in the southeastern Los Angeles coastal plain. The Central Basin is a Quaternary alluvial basin beneath the coastal plain of Los Angeles County, recharged primarily by the San Gabriel River (draining the San Gabriel Mountains granodiorite and gneiss — relatively calcium-poor crystalline rocks) and to a lesser extent the Los Angeles River and direct ocean-side precipitation. The coastal plain aquifer here is characterized by rapid hydraulic turnover and significant artificial recharge via spreading grounds at the Rio Hondo and San Gabriel River spreading grounds. The short to moderate groundwater residence times and the predominantly granitic mountain source rock produce a moderately soft finished supply.

With hardness at 75.5 mg/L, Downey residents experience light to moderate scale accumulation. Faucet aerators and showerheads develop deposits slowly — bi-monthly cleaning with citric acid solution is sufficient. Dishwashers produce clean glassware with light rinse-aid use. Hot water systems remain largely scale-free. City of Downey Public Works and CBMWD consistently deliver water meeting all California SWRCB and EPA Safe Drinking Water Act requirements.