Oconomowoc Water Hardness & Quality Report (2026)

Oconomowoc Water Utility, operated by the City of Oconomowoc in Waukesha County, Wisconsin, provides drinking water to approximately 15,000 residents in the city and surrounding areas. The utility draws exclusively from deep groundwater wells tapping Cambrian-Ordovician sandstone aquifers; there is no surface water treatment plant. Wells are located near the utility offices at 174 E. Wisconsin Avenue, with treatment involving chlorine disinfection and basic filtration to ensure compliance with federal standards. Water Superintendent Scott Osborn, P.E., can be reached at 262-569-2196 for inquiries.

The supply originates within the Oconomowoc River watershed, part of the larger Rock River basin draining into the Mississippi. Underlying geology features Paleozoic bedrock dominated by fractured dolomites of the Silurian Niagaran Group and deep sandstones of the Cambrian Mount Simon and Ironton-Galesville formations. These carbonate and mineral-rich layers contribute dissolved calcium and magnesium, resulting in a hard supply; confined aquifer conditions preserve the geologically imprinted chemistry without dilution from surface sources.

Very hard water promotes significant limescale buildup in pipes, water heaters, dishwashers, washing machines, and coffee makers, reducing efficiency and lifespan. Soap and detergent performance suffers, requiring more product; spotting on glassware and fixtures is common after drying. Routine maintenance includes annual descaling, inspecting softener resin beds, and flushing hot water systems. A water softener is strongly recommended for all households. The 2023 Annual Water Quality Report confirms all 200+ samples met EPA and state MCLs with no violations; no PFAS or notable contaminants reported.