Folsom Water Hardness & Quality Report (2026)

Folsom, California, in Sacramento County at Folsom Lake on the American River foothills (home of Folsom State Prison and Intel's original campus), draws its municipal water supply from Folsom Lake (a Bureau of Reclamation reservoir on the American River at the Sierra Nevada foothills) via the City of Folsom Water Utility and the Sacramento County Water Agency (SCWA) regional distribution system. Folsom Lake is a major Central Valley Project water supply reservoir and flood control facility. Water hardness in Folsom measures 115.5 mg/L — classified as moderately hard.

Folsom's moderate hardness reflects the American River watershed's Sierra Nevada geology with a foothills calcareous element. The American River above Folsom Lake drains the Sierra Nevada batholith (Cretaceous granodiorite — very soft) but also the Mother Lode belt of the western Sierra foothills — the Melones Fault Zone (Jurassic–Triassic Calaveras Complex and Mariposa Formation) containing calcareous metasediment, marble lenses, and serpentinite. The Jurassic limestone and marble units of the Mother Lode belt contribute some dissolved calcium to the American River tributaries in the foothills zone (Coloma, Placerville drainage). This calcareous foothill element raises American River water hardness above the purely granitic Sierra source, producing the moderate 115.5 mg/L at Folsom Lake.

At 115.5 mg/L, Folsom residents encounter moderate scale accumulation. Faucet aerators and showerheads develop deposits after several months — monthly cleaning with citric acid solution is practical maintenance. City of Folsom Water Utility and SCWA consistently deliver water meeting all California SWRCB and EPA Safe Drinking Water Act requirements.