McHenry Water Hardness & Quality Report (2026)

The McHenry Public Works Department, under the City of McHenry, Illinois, manages the municipal water supply for approximately 21,000 residents in McHenry County. Water is sourced primarily from Lake Michigan via the Northeastern Illinois Regional Water Supply, supplemented by local groundwater wells. Intake from Lake Michigan is treated at regional facilities like the Chicago-area plants, while groundwater comes from wells tapping glacial and bedrock aquifers. Distribution covers McHenry city and parts of the county, with treatment at the city's water plant processing both sources.

The watershed encompasses the Lake Michigan basin, fed by rivers like the Fox River in McHenry County, with surface water influenced by the Great Lakes' vast catchment. Locally, groundwater interacts with Pleistocene glacial till, outwash plains, and underlying Silurian-age dolomite and limestone bedrock — including the Niagaran Series dolomites of the early Paleozoic era — characteristic of the Illinois Basin. These carbonate-rich formations release calcium and magnesium through prolonged contact, yielding pronounced hardness typical of the region's carbonate terrain.

At very hard levels, scale buildup is severe, leading to over $1,400 in annual household damages from clogged pipes, reduced water heater efficiency, and stained fixtures. Water heaters, dishwashers, washing machines, and faucets accumulate calcium deposits rapidly, increasing energy bills by 20–30% and shortening appliance life. Annual descaling, vinegar rinses for showerheads, and magnetic descalers help, but a whole-house water softener is strongly recommended. McHenry maintains pH 7.5–8.5; no PFAS exceedances in recent reports; 8 contaminants slightly above health guidelines; treatment includes coagulation, filtration, chlorination, and corrosion control.