Northbrook Water Hardness & Quality Report (2026)

The Village of Northbrook Public Works Department operates the water utility serving approximately 35,000 residents in Northbrook, Cook County, Illinois, within the Chicago metropolitan area. The primary source is Lake Michigan, purchased from the City of Chicago's Jensen Water Treatment Plant and processed through the Village's own Northbrook Water Treatment Plant before distribution. The service area covers Northbrook's 13.8 square miles, including residential, commercial, and industrial users, with surface water dominating the supply.

The Lake Michigan watershed encompasses glacial drift over Paleozoic bedrock, notably Silurian dolomite and limestone like the Niagaran Series, which dissolve to impart minerals. The lake's chemistry reflects moderate mineralization from upstream drainage and shoreline geology. Northbrook's proximity to the lake yields a hard supply influenced by these carbonate rocks, sharing northern Illinois traits of dissolved calcium and magnesium ions from ancient formations, with potential groundwater supplements from shallower glacial drift aquifers adding further mineralization.

At hard levels, scale buildup affects water heaters, dishwashers, washing machines, and faucets, reducing efficiency and lifespan. White deposits on fixtures and reduced soap lathering are common. Regular descaling, vinegar rinses, and professional maintenance help mitigate issues; a water softener is recommended for households to prevent appliance damage and extend plumbing life. The 2022 Consumer Confidence Report notes routine testing for over 120 contaminants with no MCL violations, though two contaminants exceed EPA health guidelines (MCLGs) — filter recommendations apply especially for vulnerable groups. Uranium is noted as naturally occurring.