Corona Water Hardness & Quality Report (2026)

Corona, California receives its municipal water supply from the City of Corona Water Division, blending locally pumped groundwater from the Temescal Valley Groundwater Basin and Coldwater Basin beneath Riverside County with imported Metropolitan Water District of Southern California (MWD) water delivered via the Western Municipal Water District (WMWD) — which sources from both the Colorado River Aqueduct and the State Water Project (SWP) California Aqueduct. The Temescal Basin is recharged by Temescal Creek and artificial injection of imported water. Water hardness in Corona measures 135.5 mg/L — classified as moderately hard.

Corona's moderate hardness reflects the character of its blended supply sources. The Temescal Valley Groundwater Basin draws from Quaternary alluvial sediments deposited by Temescal Creek and Santa Ana River tributaries descending from the Santa Ana Mountains — the Peninsular Ranges' Mesozoic granitic and metavolcanic terrain. These alluvial sediments contribute moderate dissolved calcium from weathered feldspar-rich granite sand. Colorado River imports add significant mineral loads from canyon carbonate geology, while SWP water dilutes the blend somewhat. The resulting moderately hard supply is consistent with the broader Inland Empire region.

With hardness at 135.5 mg/L, Corona residents encounter regular scale accumulation. Faucet aerators and showerheads develop deposits within a few months — monthly cleaning with citric acid solution keeps them in good working order. Kettles benefit from periodic descaling, and dishwashers produce significantly cleaner glassware with rinse-aid. Water heaters benefit from an annual inspection for element scale. Corona Water Division consistently delivers water meeting all California SWRCB and EPA Safe Drinking Water Act requirements throughout the city's distribution network.