The city of Chicago’s drinking water system serves nearly 3 million people, making it one of the largest water utilities in the U.S. With the release of the 2025 update of EWG’s Tap Water Database, we took a closer look at this expansive system for the millions of Chicagoans served by it and compared it to the country as a whole.
In addition to information about Chicago’s drinking water quality, the Tap Water Database provides details about chemical and radioactive contaminants in the water of nearly 50,000 community systems nationwide.
It also shows how these concentrations compare to federal legal limits and EWG’s health-based standards for protection against harms such as a greater risk of cancer.
Chicago’s water supply comes from Lake Michigan and is piped to the city’s taps after treatment.
As of 2024, test results showed 20 contaminants were found in Chicago’s system, with 13 at levels above EWG’s health-based limits.
Key contaminants in Chicago tap water
Nitrate
The fertilizer chemical nitrate is found in Chicago’s water at levels two times EWG’s health guideline. Studies in the U.S. and other countries have found greater incidence of colorectal, ovarian, thyroid, kidney and bladder cancer among people exposed to nitrate in drinking water.
Despite being mostly associated with rural areas, nitrate can be a problem for both rural and urban water systems, according to EWG analyses. High nitrate levels in large cities’ water systems can result from upstream pollution from farms, stormwater runoff or the release of municipal wastewater into waterways.
A 2019 peer-reviewed study by EWG found that nitrate pollution in U.S. drinking water may cause up to 12,594 cases of cancer a year, at a cost of up to $1.5 billion for health care.
Hexavalent chromium
Hexavalent chromium, or chromium-6, was detected in Chicago’s water at almost 10 times EWG’s health guideline. A 2008 National Toxicology Program study found that water contaminated with chromium-6 causes cancer in laboratory animals, and a 2015 study by researchers in California revealed an increased risk of stomach cancer in workers exposed to the contaminant.
EWG has long raised the alarm on chromium-6, releasing a landmark analysis and map of the contamination across the U.S. in 2016. EWG maintains the interactive map, which charts contamination utility by utility.
Chromium-6 levels in Chicago’s water are about half the national and state averages. California passed a state-level contaminant limit for hexavalent chromium in 2024.
Lead
According to EWG’s analysis of 2023 lead test results, 90 percent of tested Chicago households had concentrations below 15 parts per billion, which is the federal lead action level. Only one of the 50 tests exceeded the action level.
Lead contamination can vary considerably from neighborhood to neighborhood within a city, depending on infrastructure and plumbing materials.
Aging infrastructure is often a key indicator of potential lead contamination in urban areas, since lead pipes were once used in hundreds of cities, most commonly in water lines installed before the 1930s.
Lead is a potent neurotoxin that impairs children’s intellectual development and alters their behavior and ability to concentrate. There is a strong scientific agreement that any amount of lead exposure during childhood is harmful and irreversible.
If you live in Chicago and would like to find out more about lead in your tap water, contact the city and ask for a free test kit. Additionally, you can visit Lead-Safe Chicago to learn more about how the city is remediating lead hazards.
Radium
Chicago's water contains radium at levels 18 times higher than the EWG health guideline. Radium is a radioactive element that often occurs naturally in rocks and soil, and it is linked to bone cancer and other cancer.
Disinfection byproducts
Chicago’s utility page in the Tap Water Database shows that nine of the 13 contaminants that exceed EWG’s health guidelines are disinfection byproducts, an umbrella term that includes bromodichloromethane, chloroform, dibromoacetic acid, dibromochloromethane, dichloroacetic acid, the haloacetic acids HAA5 and HAA9, total trihalomethanes and trichloroacetic acid.
Drinking water must be disinfected to kill disease-causing pathogens, and the process is one of the greatest accomplishments in public health. But it can produce toxic byproducts if the water contains organic matter such as soil, fertilizer and animal waste – all of which are likely present in Chicago’s untreated water.
Scientists have identified more than 600 disinfection byproducts in treated drinking water. Some of the most common are linked to DNA damage, cancer and other harms. In a 2020 study, researchers in Sweden found that pregnant women exposed to low levels of disinfection byproducts in chlorinated drinking water were more likely to give birth to underweight babies.
Water filtration
EWG’s Tap Water Database can help you find the right water filter for your needs. On a utility’s page in the database, you can see what contaminants were found in the system that could be addressed by a particular type of filter.
Most of the Chicago system’s contaminants that fall above EWG’s health guidelines can be reduced effectively by a simple countertop carbon filter.
The exceptions are chromium-6, nitrate and radium. Results of recent EWG tests of home filters found some pitcher filters can reduce levels of these contamination.
An advanced filter such as reverse osmosis is the most effective way to remove contaminants from drinking water – but this can cost more upfront than a typical carbon filter.
If you’re in the market for a countertop carbon filter, make sure to check out EWG’s guide to countertop water filters.
Stay in the know
EWG’s Tap Water Database is a helpful tool, even if you’re not a Chicagoan.
The database puts your tap water’s contamination into perspective, so you can make informed decisions to reduce your exposure. Once you find your utility in the database, the info about local water quality can help you understand what’s in it. Then you can make informed decisions about how best to reduce your exposure to contaminants.
In the weeks and months ahead, EWG will continue to produce original drinking water content, from scientific analyses to everyday solutions to eye-opening explainers. Stay in the know by subscribing to EWG’s email list and follow us on Facebook, Instagram and YouTube.
