Evanston Water Hardness & Quality Report (2026)

The City of Evanston Water Division operates the Evanston Water Treatment Plant, located on the shores of Lake Michigan in Cook County, Illinois. The utility sources all drinking water from Lake Michigan, the second-largest Great Lake by volume and the only one entirely within the United States. The treatment facility has a capacity of 108 million gallons per day and serves Evanston's population of approximately 75,994, as well as the Village of Skokie and the Northwest Water Commission — which includes Arlington Heights, Buffalo Grove, Palatine, and Wheeling.

Evanston's water supply originates from the Lake Michigan watershed, shaped by Pleistocene glaciation and underlain by Ordovician-age carbonate bedrock including dolomite and limestone. The lake's water reflects dissolution of these carbonate minerals and glacial deposits across the Great Lakes basin, resulting in a hard supply. Although Lake Michigan is a surface-water source with lower mineral concentrations than typical groundwater, the regional carbonate geology still imparts a hard character to the finished water.

Hard water in Evanston causes scale buildup on fixtures, reduces soap and detergent efficiency, and accelerates wear on water heaters and dishwashers. The utility does not operate a municipal softening plant, so residents requiring softened water must install point-of-use or whole-house systems. A water softener is recommended for households with sensitive appliances. Treatment at the plant involves collection via three intakes, coagulation and flocculation, chlorination for disinfection, fluoridation, phosphate addition to inhibit lead and copper leaching, sand filtration, and activated carbon treatment for taste and odor — particularly during warm-weather months when algal activity in Lake Michigan increases.