Cottage Grove Water Hardness & Quality Report (2026)

Cottage Grove, Minnesota, in Washington County — a major south Washington County suburban community in the St. Paul–South Metro corridor (Cottage Grove is one of the larger south Washington County communities in the rapidly growing Twin Cities southeast suburban corridor), home of 3M's main manufacturing campus (3M Company — formerly Minnesota Mining and Manufacturing, one of the world's largest diversified manufacturers, has a major manufacturing and research complex in Cottage Grove), a rapidly growing suburban community in the expanding Washington County I-494 corridor, and a diverse Washington County community — draws its municipal water supply from the deep Cambrian–Ordovician aquifer wells via the City of Cottage Grove Water Division. Water hardness in Cottage Grove measures 199 mg/L — classified as hard.

Cottage Grove's hard supply reflects the Washington County Paleozoic carbonate aquifer's highly calcareous geology. The Jordan Sandstone and Prairie du Chien Dolomite at Cottage Grove–Washington County draws from: the Cambrian Jordan Sandstone (calcareous-moderate deep aquifer); the Ordovician Prairie du Chien Dolomite (highly calcareous dolomite — the primary carbonate aquifer of the St. Paul metro); and the Wisconsin Age calcareous Superior Lobe till (calcareous glacial deposits). City of Cottage Grove treatment produces the hard 199 mg/L.

At 199 mg/L, Cottage Grove residents face regular hard water challenges. Monthly descaling with citric acid solution is recommended. City of Cottage Grove Water Division consistently delivers water meeting all Minnesota PCA and EPA Safe Drinking Water Act requirements.