Markham Water Hardness & Quality Report (2026)

Markham Water Department, operated by the City of Markham in Cook County, Illinois, supplies drinking water to about 12,000 residents in the southern Chicago suburbs. The primary source is Lake Michigan, accessed through the City of Chicago's regional distribution system, with potential minor groundwater augmentation. Water undergoes conventional treatment, including filtration and disinfection, at upstream Chicago facilities before reaching Markham residents. The Lake Michigan watershed, spanning over 118,000 square miles, is fed by rivers like the Grand, St. Clair, and Niagara. The water's character is significantly shaped by glacial geology from the last Ice Age.

Pleistocene glacial deposits cover Paleozoic bedrock, including Ordovician dolomites and limestones. These rocks dissolve sparingly into surface waters, creating a very soft base chemistry. However, any groundwater components drawn from shallow aquifers in the region can interact with these same carbonate formations. This interaction imparts a harder, more mineralized character through natural leaching, resulting in an overall moderately mineralized to hard water supply for Markham.

When water is very hard, scale buildup can accelerate in appliances like water heaters, dishwashers, boilers, and coffee makers, reducing their efficiency by as much as 50% and shortening their lifespan. Homeowners might notice white calcium deposits on faucets and fixtures. Laundry and dish detergents may not perform as well, potentially leaving residues. Regular maintenance, such as deliming heaters every one to two years, installing scale-inhibiting filters, and using high-efficiency detergents, can help mitigate these issues. A whole-house water softener is often recommended for very hard water to prevent appliance damage and improve soap efficiency. The City of Markham's 2024 Water Quality Report indicates compliance with EPA standards, though some third-party analyses have noted contaminants exceeding health guidelines. Using a filter is advised for optimal safety.