Spokane Valley Water Hardness & Quality Report (2026)

Spokane Valley, Washington, the second-largest city in Eastern Washington in Spokane County, draws its municipal water supply from groundwater wells tapping the Spokane Valley–Rathdrum Prairie Aquifer (SVRP Aquifer) — one of the largest and highest-quality unconfined aquifers in the Pacific Northwest — through multiple utility providers including the Consolidated Irrigation District, Vera Water and Power, and Model Irrigation District in Spokane County. The SVRP Aquifer extends from the Idaho border westward through Spokane Valley. Water hardness measures 55.5 mg/L — classified as moderately soft.

Spokane Valley's moderately soft supply reflects the remarkable geology of the SVRP Aquifer. The Spokane Valley–Rathdrum Prairie Aquifer is a Quaternary glaciofluvial gravel aquifer — formed by the catastrophic Missoula Floods (repeated glacial outburst floods during the last Ice Age, 15,000–20,000 years ago) that scoured the Columbia Plateau and deposited immense volumes of clean, washed gravel and cobbles across the Spokane Valley. This glaciofluvial gravel is derived from the Coeur d'Alene Mountains quartzite, granite, and gneiss of the Idaho Selkirk Mountains and the Spokane River Columbia River Basalt terrain — predominantly siliceous, low-calcium parent rock. The rapid groundwater flow through the coarse gravel limits carbonate equilibration, maintaining very soft water quality.

With hardness at 55.5 mg/L, Spokane Valley residents experience minimal scale challenges. Faucet aerators and showerheads develop deposits slowly — bi-monthly cleaning with citric acid solution is sufficient. Dishwashers produce clean glassware. Local water utilities and Spokane County consistently deliver water meeting all Washington DOH and EPA Safe Drinking Water Act requirements.