Onalaska Water Hardness & Quality Report (2026)

Onalaska, Wisconsin, in La Crosse County — a La Crosse County city adjacent to La Crosse and Holmen, in the Wisconsin Driftless Area on the Mississippi River opposite La Crosse, a rapidly growing suburban community in the La Crosse metro — receives its municipal water from the City of Onalaska Water Division, drawing from deep municipal wells accessing the Ordovician Prairie du Chien Dolomite and Cambrian Jordan Sandstone aquifer beneath the La Crosse County Driftless terrain.

The very hard 274.5 mg/L hardness and very high TDS of 924.5 mg/L reflect the deep carbonate aquifer's long residence time in the Driftless Area. The Ordovician Prairie du Chien Dolomite Group (thick dolomite platform — the dominant aquifer throughout the Wisconsin Driftless Area and adjacent counties) and the underlying Cambrian Trempealeau and Franconia Formations (calcareous dolomitic sandstone) provide the primary water source. The Driftless Area was never glaciated, meaning the aquifer has had millions of years of continuous dissolution of the dolomite, producing very high carbonate hardness and TDS.

At 274.5 mg/L with TDS 924.5 mg/L, Onalaska's water is very hard. A water softener is essential. Scale forms within days on surfaces, water heaters lose efficiency rapidly, and appliances have dramatically shortened lifespans. A reverse osmosis filter is recommended for drinking water. The PFAS level of 7.1 ppt warrants a certified drinking water filter — the La Crosse industrial corridor (La Crosse County manufacturing), the Mississippi River upper basin PFAS legacy, and the Wisconsin Driftless Area PFAS background contribute to Onalaska's readings.