The tap water delivered by the City of Chicago meets or exceeds the regulatory requirements set by the U.S. Environmental Protection Agency (EPA) and the Illinois EPA. The city’s rigorous treatment process ensures the water leaving the purification plants is safe for consumption. However, the safety of the water at the tap is complicated by the presence of aging infrastructure, particularly the lead service lines that connect the municipal water mains to many residential properties. While the public water supply is high quality, the final water quality in older homes can be compromised, making filtration and testing a prudent step for residents.
How Chicago Water is Sourced and Treated
Chicago draws its entire water supply from Lake Michigan using an extensive system of intake cribs and tunnels. This raw water is transported to one of the city’s two treatment facilities: the Jardine Water Purification Plant and the Eugene Sawyer Water Purification Plant. The treatment process is a multi-step procedure designed to clean and disinfect the water before it enters the distribution system.
Initial steps involve screening out debris, followed by coagulation using chemicals like aluminum sulfate and polymer to bind fine particles into larger clumps called floc. The water then moves through sedimentation basins where these floc particles settle out, and finally through filters made of sand and gravel. Chemical treatment involves disinfection with chlorine. Blended polyphosphate is also added to coat the inside of distribution pipes, which helps control corrosion and minimize the leaching of metals like lead.
Primary Regulatory Concerns and Contaminants
The Chicago Department of Water Management (DWM) constantly monitors water quality, testing for regulated contaminants to ensure compliance with federal and state standards. Chicago consistently reports meeting all mandated drinking water standards, a status detailed annually in the Consumer Confidence Report (CCR) provided to residents. This strong compliance record reflects the effectiveness of the city’s source water protection and treatment processes.
Beyond regulated standards, other contaminants are monitored by independent health organizations. Disinfection byproducts (DBPs), such as haloacetic acids (HAA5) and trihalomethanes (TTHMs), are formed when chlorine reacts with organic material. While Chicago’s levels of these byproducts fall within the EPA’s legal limits, some analyses suggest they exceed stricter, health-based guidelines. The city also monitors for emerging contaminants like Per- and Polyfluoroalkyl Substances (PFAS) and Chromium-6.
The Critical Issue of Residential Lead Service Lines
The principal threat to tap water quality occurs not in the municipal system but within the private service lines and home plumbing. Chicago has the highest number of lead service lines (LSLs) in the country, with an estimated 400,000 to 412,000 lines connecting the city’s water mains to properties. This prevalence is due to a historic city ordinance that mandated the use of lead pipes for these connections until the federal ban in 1986.
LSLs run from the water main under the street to the building’s plumbing system. Although the city uses polyphosphate to create a protective coating and prevent lead from leaching, this coating can be temporarily disrupted. Disturbances like nearby construction, plumbing repairs, or water meter replacement can cause lead particles to flake off into the water supply. Lead levels also increase when water remains stagnant in the pipes for several hours, such as overnight.
The city is actively addressing this infrastructure challenge through replacement programs. The Equity Lead Service Line Replacement (E-LSLR) Program offers free replacement to income-qualified, owner-occupied residential buildings of one to two units. The Homeowner-Initiated Program provides a permit fee waiver for residents who hire their own contractors. Even with these efforts, the timeline for full replacement extends decades into the future, making localized mitigation measures necessary for many residents.
Steps for Home Water Testing and Filtration
For residents concerned about water quality, specific actions can confirm safety and mitigate risk. The City of Chicago offers a free residential water lead testing kit, which can be requested by calling 311 or visiting the DWM website. This testing is conducted by a certified laboratory and provides a precise snapshot of the lead concentration in the home’s water.
If testing reveals elevated lead levels, or as a proactive measure, installing a point-of-use water filter can significantly reduce exposure. Select a filter specifically certified by an accredited third-party organization, such as NSF International, to meet the NSF/ANSI Standard 53. This certification confirms the filter’s capability to reduce lead to safe levels. Common options include pitcher filters, faucet-mounted units, and under-sink systems, all of which must be maintained and have their cartridges replaced according to manufacturer’s instructions.