Mount Prospect Water Hardness & Quality Report (2026)

Mount Prospect, Illinois, in northwest Cook County — a major northwest Chicago suburb adjacent to O'Hare International Airport, with a substantial Filipino-American and Korean-American community and a traditional Illinois mid-century bungalow residential character — draws its municipal water supply from Lake Michigan via the City of Chicago Department of Water Management (DWM), distributed wholesale to the Village of Mount Prospect Public Works Water Division through the northwest Cook County suburban water grid. Water hardness in Mount Prospect measures 177 mg/L — classified as hard.

Mount Prospect's hard supply — harder than the Chicago DWM source — reflects the northwest Cook County Lake Michigan distribution infrastructure characteristics. Mount Prospect is served through the Chicago DWM wholesale distribution system and the Village's own northwest suburban distribution grid. Mount Prospect developed as a northwest suburban community in the 1920s–1950s, with distribution mains of the post-World War II suburban build-out era. The DWM wholesale transmission through the northwest suburban grid and Mount Prospect's own cast-iron mains accumulate substantial mineral content, producing the hard 177 mg/L — elevated well above the Lake Michigan source hardness.

At 177 mg/L, Mount Prospect residents face regular hard water challenges. Scale deposits form on faucet aerators, showerheads, and appliances within weeks — monthly descaling with citric acid solution is standard maintenance. Village of Mount Prospect Public Works Water Division consistently delivers water meeting all Illinois EPA and federal EPA Safe Drinking Water Act requirements.