Illinois Water Quality Report
Tap water quality data for 10 cities in Illinois, updated 2026.
US average: 100 ppm
4 of 10 cities violation-free
10 cities tested
10 water systems tracked
Cleanest Tap Water in Illinois
Cities with the fewest water quality issues
Aurora
183K served
Champaign
151K served
Peoria
138K served
East St Louis
132K served
Naperville
155K served
Chicago
2.7M served
Rockford
148K served
Elgin
116K served
Springfield
129K served
Joliet
169K served
Most Water Quality Issues in Illinois
Cities with the most violations and concerns
Joliet
169K served
Springfield
129K served
Elgin
116K served
Chicago
2.7M served
Rockford
148K served
Naperville
155K served
Water Hardness Across Illinois
Not sure what your hardness means? Use our Water Hardness Calculator or find the best hardness test kits.
Illinois Tap Water: What You Need to Know
Illinois has 10 tracked water utilities serving approximately 4.1M residents. The average water hardness is 285 ppm (16.7 GPG), classified as Very Hard — above the national average of 100 ppm. Hardness ranges from 183 ppm in Chicago to 324 ppm in Rockford.
In the past 3 years, 6 of 10 cities in Illinois have recorded water quality violations, totaling 510 violations (0 health-based). All 10 tested cities have lead levels below the EPA action level of 15 ppb.
With very hard water on average, many Illinois residents may notice mineral buildup on fixtures, dry skin, or stiff-feeling hair. A shower filter for hard water can help reduce chlorine exposure, while a water softener addresses the mineral buildup directly.
Frequently Asked Questions About Illinois Water
Is tap water safe to drink in Illinois?
Most tap water in Illinois meets EPA standards, but 6 cities have recorded violations in the past 3 years (0 health-based). We recommend checking your specific city's report on TapWater.org and considering a home water test.
How hard is the water in Illinois?
Illinois's average water hardness is 285 ppm (16.7 GPG), classified as Very Hard. This is above the national average of 100 ppm. Hardness varies significantly by city — use our Water Hardness Calculator to check your specific area.
Which city in Illinois has the cleanest tap water?
Based on EPA violation data, lead testing, and water quality metrics, Aurora ranks as having the cleanest tap water in Illinois. It has zero violations in the past 3 years.
Which city in Illinois has the most water quality issues?
Joliet currently has the most water quality concerns in Illinois, with 412 violations in the past 3 years. Residents should check their city's detailed water quality report and consider using a certified water filter.
Where does Illinois get its water from?
The majority of Illinois's water systems (60%) use surface water as their primary source. Surface water comes from rivers, lakes, and reservoirs. Each city's specific source can vary — check individual city reports for details.
All 10 Cities
Sorted by population served
Chicago
Utility serves 2.7M
Aurora
Utility serves 183K
Joliet
Utility serves 169K
Naperville
Utility serves 155K
Champaign
Utility serves 151K
Rockford
Utility serves 148K
Peoria
Utility serves 138K
East St Louis
Utility serves 132K
Springfield
Utility serves 129K
Elgin
Utility serves 116K