Chico Water Hardness & Quality Report (2026)

Chico, California — home to California State University, Chico — draws its municipal water supply through the City of Chico Water Department, sourcing primarily from local groundwater wells in the Sacramento Valley floor and lower Sierra Nevada foothills, tapping the Tuscan Formation alluvial fan aquifer and the Tehama Formation gravel aquifer in Butte County. Big Chico Creek, draining the nearby Sierra Nevada foothills, recharges the local shallow alluvial aquifer used by Chico municipal wells. The city also maintains access to State Water Project deliveries during dry periods. Water hardness in Chico measures 80.5 mg/L — classified as moderately soft.

Chico's moderately soft supply reflects the alluvial and volcanic geology of the upper Sacramento Valley foothills zone. Local groundwater wells tap the Tuscan Formation — a Pliocene–Pleistocene volcanic alluvial fan deposit of andesitic gravel and sand derived from the Cascade Range and upper Sierra Nevada foothills — and the Tehama Formation (older Pliocene gravel and sand). These formations are dominated by volcanic andesite, basalt, and granitic detritus with limited calcareous cement, contributing modest dissolved calcium. Big Chico Creek recharge originates from the Sierra Nevada granite and metavolcanic belt, carrying inherently soft snowmelt that helps maintain the moderately soft finished groundwater.

With hardness at 80.5 mg/L, Chico residents experience minimal to moderate scale challenges. Faucet aerators and showerheads develop light deposits over extended periods — bi-monthly cleaning with citric acid solution is sufficient. Dishwashers produce clean glassware with light rinse-aid use. Hot water systems accumulate minimal scale. City of Chico Water Department consistently delivers water meeting all California SWRCB and EPA Safe Drinking Water Act requirements.