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Not health advice. Contact your local water utility for concerns.
Data from EPA Water Quality Reports. For official information, contact your water utility or health department.
Water quality data for 22 cities serving 3,884,861 residents
Cook County in Illinois has an average water quality score of 92/100 (Grade A) based on analysis of 22 municipal water systems. The county's water systems serve approximately 3,884,861 residents.
Overall, Cook County demonstrates good water quality standards. 16 of 22 cities exceed the county average, with Streamwood leading with a score of 100/100.
22 cities ranked by water quality score
| Rank | City | Score | Grade | Population |
|---|---|---|---|---|
| 1 | Orland Park | 100 | A | 58,020 |
| 2 | Hoffman Estates | 100 | A | 50,179 |
| 3 | Wheeling | 100 | A | 39,725 |
| 4 | Streamwood | 100 | A | 39,577 |
| 5 | Hanover Park Biggest deduction: 1 monitoring/reporting violation in the last 5 years (−1 pts) | 99 | A | 37,470 |
| 6 | Tinley Park Biggest deduction: 2 monitoring/reporting violations in the last 5 years (−2 pts) | 98 | A | 56,703 |
| 7 | Schaumburg Biggest deduction: 3 monitoring/reporting violations in the last 5 years (−3 pts) | 97 | A | 75,750 |
| 8 | Evanston Biggest deduction: Lead 90th-percentile tap result 8 ppb for 2025-07-01–2025-12-31, below the 15 ppb action level (−3 pts) | 97 | A | 74,486 |
| 9 | Palatine Biggest deduction: Lead 90th-percentile tap result 7.5 ppb for 2026-01-01–2026-06-30, below the 15 ppb action level (−3 pts) | 97 | A | 70,875 |
| 10 | Berwyn Biggest deduction: 3 monitoring/reporting violations in the last 5 years (−3 pts) | 97 | A | 57,250 |
| 11 | Oak Park Biggest deduction: Lead 90th-percentile tap result 5.08 ppb for 2025-07-01–2025-12-31, below the 15 ppb action level (−3 pts) | 97 | A | 54,583 |
| 12 | Oak Lawn Biggest deduction: Lead 90th-percentile tap result 8.1 ppb for 2026-01-01–2026-06-30, below the 15 ppb action level (−3 pts) | 96 | A | 58,362 |
| 13 | Glenview Biggest deduction: Lead 90th-percentile tap result 9.8 ppb for 2025-07-01–2025-12-31, below the 15 ppb action level (−3 pts) | 95 | A | 47,856 |
| 14 | Mount Prospect Biggest deduction: 5 monitoring/reporting violations in the last 5 years (−5 pts) | 95 | A | 41,000 |
| 15 | Park Ridge Biggest deduction: Lead 90th-percentile tap result 6.79 ppb for 2026-01-01–2026-06-30, below the 15 ppb action level (−3 pts) | 95 | A | 39,800 |
| 16 | Skokie Biggest deduction: 4 monitoring/reporting violations in the last 5 years (−4 pts) | 93 | A | 66,422 |
| 17 | Chicago Biggest deduction: 9 monitoring/reporting violations in the last 5 years (−9 pts) | 88 | B | 2,721,308 |
| 18 | Arlington Heights Biggest deduction: 21 monitoring/reporting violations in the last 5 years (−10 pts) | 87 | B | 73,320 |
| 19 | Des Plaines Biggest deduction: Lead 90th-percentile tap result 11.1 ppb for 2026-01-01–2026-06-30, below the 15 ppb action level (−10 pts) | 87 | B | 60,675 |
| 20 | Cicero Biggest deduction: 1 health-based violation (MCL/treatment-technique) in the last 5 years (−10 pts) | 83 | B | 83,000 |
| 21 | Bartlett Biggest deduction: Lead 90th-percentile tap result 22.6 ppb for 2025-07-01–2025-12-31, above the 15 ppb federal action level (−25 pts) | 75 | C | 41,500 |
| 22 | Calumet City Biggest deduction: 1 health-based violation still unresolved with EPA/state (−20 pts) | 55 | F | 37,000 |
Real EPA readings across county water systems (lead: latest 90th percentile; PFAS: UCMR5 2023–2026; others: 2012–2019 averages)
| Contaminant | Avg Level | Max Level | EPA Limit | % of Limit | Cities |
|---|---|---|---|---|---|
| Lead (90th percentile) | 6.094 ppb | 22.6 ppb | 15 ppb | 40.6% | 22 |
| TTHM (2012–2019 avg) | 30.45 ug/L | 47.841 ug/L | 80 ug/L | 38.1% | 22 |
| Radium (2012–2019 avg) | 1.251 pCi/L | 2.093 pCi/L | 5 pCi/L | 25% | 3 |
| HAA5 (2012–2019 avg) | 14.595 ug/L | 24.283 ug/L | 60 ug/L | 24.3% | 22 |
| Fluoride (2012–2019 avg) | 0.818 mg/L | 0.936 mg/L | 4 mg/L | 20.4% | 3 |
| Nitrate (2012–2019 avg) | 0.334 mg/L | 0.388 mg/L | 10 mg/L | 3.3% | 3 |
| Arsenic (2012–2019 avg) | 0.206 ug/L | 0.464 ug/L | 10 ug/L | 2.1% | 3 |
| PFAS (PFOA/PFOS max, UCMR5) | 0 ppt | 0 ppt | 4 ppt | 0% | 22 |
Recent violations across county water systems
Health-based: Treatment technique — LSL Inventory - LEAD AND COPPER RULE REVISIONS
10/16/2024
Health-based: MCL exceeded — Maximum Contaminant Level Violation, E. coli (RTCR) - Revised Total Coliform Rule
8/31/2019
Health-based: MCL exceeded — Maximum Contaminant Level Violation, E. coli (RTCR) - Revised Total Coliform Rule
5/31/2019
Monitoring & reporting — Follow-up Or Routine LCR Tap M/R - Lead and Copper Rule
12/31/2025
Showing 10 of 20 recent violations
Water quality in Cook County, Illinois reflects the region's unique combination of water sources, treatment infrastructure, and environmental factors. Our comprehensive analysis examines 22 municipal water systems serving a combined population of over 3,884,861 residents.
The county shows strong water quality performance, with scores ranging from 55/100 in Calumet City to 100/100 in Streamwood. This 45-point spread indicates significant variation in water quality across the county, suggesting different water sources or treatment approaches.
The most prevalent contaminants detected across Cook County water systems include Lead (90th percentile), TTHM (2012–2019 avg), Radium (2012–2019 avg). Every county-wide average sits below 50% of its EPA Maximum Contaminant Level (MCL).
Cook County's water quality is generally good. Residents can feel confident in their tap water quality, though those with specific health concerns or sensitivity to certain contaminants may still benefit from filtration. Regular review of your city's annual Consumer Confidence Report is recommended.
Cook County has an average water quality score of 92/100 (Grade A) based on analysis of 22 municipal water systems serving 3,884,861 residents.
Streamwood has the highest water quality score in Cook County at 100/100. View the detailed report for Streamwood.
Most cities in Cook County have water that meets EPA standards. However, a water filter can provide additional protection and improve taste. The need depends on your specific city and any personal health considerations.
Click on any city in the rankings table above to view its detailed water quality report, including contaminant levels, EPA compliance history, and filter recommendations.