Vallejo Water Hardness & Quality Report (2026)

Vallejo, California, in Solano County at the northern San Francisco Bay, draws its municipal water supply through the City of Vallejo Water Division, sourcing primarily from the Solano Project — operated by the Solano Irrigation District — delivering water from Lake Berryessa (Putah Creek, Napa County) via the Putah South Canal and the Vallejo–Benicia pipeline system. Lake Berryessa is the major water supply reservoir for Solano County, impounding runoff from the Inner Coast Range in Lake and Napa Counties. Water hardness in Vallejo measures 44.5 mg/L — classified as soft, one of the softer supplies in the greater Bay Area.

Vallejo's soft supply reflects the geology of the Lake Berryessa watershed in the Northern California Coast Range. The Putah Creek watershed and Lake Berryessa basin drain the Coast Range Inner Valleys and Knoxville Highlands of Lake and Napa Counties — terrain dominated by the Jurassic–Cretaceous Franciscan Complex (chert, greywacke sandstone, argillite, and greenstone) and Knoxville Formation ultramafic and serpentinite bodies. These Franciscan Complex rocks — exotic oceanic terrane accreted to North America during subduction — are characteristically calcium-poor and siliceous, contributing minimal dissolved calcium bicarbonate to watershed drainage. The Coast Range climate and relatively rapid runoff further limit mineral dissolution from these resistant, calcium-depleted formations.

With hardness at 44.5 mg/L, Vallejo residents experience minimal scale challenges in household use. Faucet aerators and showerheads rarely need descaling. Soap and shampoo lather very well with modest product amounts. Dishwashers produce clean glassware. Hot water systems remain largely scale-free. City of Vallejo Water Division and Solano Irrigation District consistently deliver water meeting all California SWRCB and EPA Safe Drinking Water Act requirements.