Oshkosh Water Hardness & Quality Report (2026)

Oshkosh, Wisconsin, the Winnebago County seat on the south shore of Lake Winnebago — 'Sawdust City', home of the EAA AirVenture annual fly-in and the University of Wisconsin–Oshkosh — draws its municipal water supply from Lake Winnebago via the City of Oshkosh Water Utility, treating Lake Winnebago water at the Oshkosh Water Treatment Plant. Lake Winnebago, on the Niagaran Dolomite basin, would naturally produce very hard water, but the Oshkosh Water Utility applies extensive lime softening treatment. Water hardness in Oshkosh measures 85 mg/L — classified as moderately soft, strikingly soft compared to neighboring Appleton (198.5 mg/L) on the same Lake Winnebago system.

Oshkosh's soft supply — despite drawing from the same Lake Winnebago fed by the Silurian Niagaran Dolomite watershed as Appleton (198.5 mg/L) — reflects the City of Oshkosh Water Utility's extensive lime-soda softening treatment process. The raw Lake Winnebago water is naturally very hard (200–350 mg/L from the Niagaran Dolomite drainage), but Oshkosh aggressively treats this supply through lime softening (adding lime — $Ca(OH)_2$ — to precipitate calcium carbonate and magnesium hydroxide). Oshkosh has invested in one of the most effective municipal lime-softening processes in Wisconsin, achieving a finished hardness of only 85 mg/L — a dramatic reduction from the raw source hardness. Neighboring Appleton does not use equivalent lime softening, explaining the dramatic hardness difference.

With hardness at 85 mg/L, Oshkosh residents enjoy remarkably soft water for a Wisconsin dolomite basin city. City of Oshkosh Water Utility consistently delivers water meeting all Wisconsin DNR and EPA Safe Drinking Water Act requirements.