Wisconsin Water Quality Report: 3,023 Water-System Violations Mapped to 466 ZIPs
916 water systems · 466 ZIP codes · 3,023 violations
Data: EPA Safe Drinking Water Information System (SDWIS), EPA ECHO
ZipCheckup tracks EPA drinking-water compliance for 916 public water systems serving 466 ZIP codes in Wisconsin. The state record shows 3,023 EPA violations, 766 health-based.
City Water Quality Map: Wisconsin
Each circle represents a city. Size indicates population, color indicates water quality grade. Tap a circle for details.
Cities with Most Violations in Wisconsin
| # | City | Grade | Violations | Systems | Population | |
|---|---|---|---|---|---|---|
| 1 | Waukesha | 144 | 9 | 94,161 | Details → | |
| 2 | Pewaukee | 142 | 5 | 26,652 | Details → | |
| 3 | New Berlin | 78 | 4 | 40,213 | Details → | |
| 4 | Wales | 76 | 3 | 3,073 | Details → | |
| 5 | West Bend | 71 | 7 | 49,524 | Details → | |
| 6 | Delavan | 69 | 5 | 16,056 | Details → | |
| 7 | Kewaskum | 67 | 3 | 8,223 | Details → | |
| 8 | Lake Geneva | 63 | 5 | 18,440 | Details → | |
| 9 | Madison | 62 | 16 | 308,771 | Details → | |
| 10 | Racine | 50 | 6 | 127,813 | Details → |
Most Common Contaminants in Wisconsin
| Contaminant | Category | Violations | ZIPs Affected | Health Risk |
|---|---|---|---|---|
| Public Notice Rule | Reporting | 589 | 238 | No |
| Lead and Copper Rule Revisions | Treatment Technique | 352 | 225 | Yes |
| Combined Radium (-226 and -228) | Radionuclides | 316 | 46 | Yes |
| Gross Alpha (excl. radon and uranium) | Radionuclides | 313 | 36 | Yes |
| Lead and Copper Rule | Treatment Technique | 302 | 157 | Yes |
| Consumer Confidence Rule | Reporting | 244 | 106 | No |
| Total Trihalomethanes (TTHM) | Disinfection Byproducts | 98 | 81 | Yes |
| Haloacetic Acids (HAA5) | Disinfection Byproducts | 87 | 74 | Yes |
| Nitrate | Inorganic | 47 | 38 | Yes |
| Radium-228 | Radionuclides | 42 | 27 | No |
Water Quality Overview
Wisconsin has 916 community water systems represented across 466 directly mapped ZIP records. The associated city records cover approximately 5,445,157 people. The available records contain 3,023 EPA violations, including 766 health-based violations.
Health-based violations account for 25% of all violations in Wisconsin. These violations indicate contaminant levels that may pose direct risks to human health, as opposed to monitoring or reporting failures.
Violation Breakdown
| Violation Type | Count | Percentage |
|---|---|---|
| Health-based | 766 | 25.3% |
| Monitoring/Reporting | 2,257 | 74.7% |
| Total | 3,023 | 100% |
Health-based violations are MCL, MRDL (disinfectant) and treatment-technique violations. Monitoring violations indicate failures to test or report - these do not necessarily mean unsafe water, but they mean the water was not properly verified.
Cities with Most Violations
The following cities in Wisconsin have the highest number of EPA violations:
| Rank | City | Violations | Water Systems | Population |
|---|---|---|---|---|
| 1 | Waukesha | 144 | 9 | 94,161 |
| 2 | Pewaukee | 142 | 5 | 26,652 |
| 3 | New Berlin | 78 | 4 | 40,213 |
| 4 | Wales | 76 | 3 | 3,073 |
| 5 | West Bend | 71 | 7 | 49,524 |
| 6 | Delavan | 69 | 5 | 16,056 |
| 7 | Kewaskum | 67 | 3 | 8,223 |
| 8 | Lake Geneva | 63 | 5 | 18,440 |
| 9 | Madison | 62 | 16 | 308,771 |
| 10 | Racine | 50 | 6 | 127,813 |
Violation counts are cumulative across all water systems serving each city. Higher counts may reflect larger systems with more monitoring requirements, not necessarily worse water quality.
Violation Trend Over Time
Year-by-year EPA violations recorded across all water systems in Wisconsin:
| Year | Health-based violations |
|---|---|
| 2021 | 63 |
| 2022 | 73 |
| 2023 | 104 |
| 2024 | 304 |
| 2025 | 71 |
| 2026 | 15 |
Health-based violations have decreased from 63 in 2021 to 15 in 2026, suggesting improving compliance across Wisconsin.
Most Common Contaminants
The following contaminants have caused the most violations across Wisconsin water systems:
| Contaminant | Category | Violations | ZIPs Affected | Health-Based |
|---|---|---|---|---|
| Public Notice Rule | Reporting | 589 | 238 | No |
| Lead and Copper Rule Revisions | Treatment Technique | 352 | 225 | Yes |
| Combined Radium (-226 and -228) | Radionuclides | 316 | 46 | Yes |
| Gross Alpha (excl. radon and uranium) | Radionuclides | 313 | 36 | Yes |
| Lead and Copper Rule | Treatment Technique | 302 | 157 | Yes |
| Consumer Confidence Rule | Reporting | 244 | 106 | No |
| Total Trihalomethanes (TTHM) | Disinfection Byproducts | 98 | 81 | Yes |
| Haloacetic Acids (HAA5) | Disinfection Byproducts | 87 | 74 | Yes |
| Nitrate | Inorganic | 47 | 38 | Yes |
| Radium-228 | Radionuclides | 42 | 27 | No |
How to Check Your Water in Wisconsin
Enter your ZIP code on ZipCheckup for detailed water-system data including contaminant levels and violation history; the separate Home Safety Score is a multi-source index
Request your CCR - every water utility must provide an annual Consumer Confidence Report
Get a home test - certified kits ($20-$50) or professional lab tests ($150-$400)
Consider filtration - NSF-certified filters can address specific contaminants found in your area
EPA Enforcement
The EPA and state regulators have taken enforcement actions against water systems in Wisconsin. Enforcement actions range from compliance assistance to formal orders and penalties.
Data Sources
- Water quality: EPA Safe Drinking Water Information System (SDWIS)
- Enforcement: EPA ECHO
Updated daily.
What are EPA violations?
Health-based violations are EPA violations of a Maximum Contaminant Level (MCL), a Maximum Residual Disinfectant Level (MRDL) or a required treatment technique - the enforceable standards designed to protect human health. Wisconsin has 766 such violations across its water systems. Not all violations cause illness; review each violation type and duration to understand possible health implications.
Understanding water quality grades
ZipCheckup grades water systems from A to F based on EPA violation history, contaminant levels, and system compliance. Grades summarize ZipCheckup's scoring inputs; review the underlying records for specific issues. Grades are calculated per ZIP code and aggregated at the city, county, and state level.
Wondering about your tap water?
Water quality varies by ZIP code. Enter yours to see contaminant data, violations, and filtration recommendations specific to your area.
Check Your ZIP Code Water Quality →Frequently Asked Questions
Is the tap water safe to drink in Wisconsin?
Records for 916 community water systems mapped to ZIPs in Wisconsin show 3,023 reported violations, including 766 health-based. Water quality varies by city and ZIP code - check your specific location for detailed results.
How many violations are on record for water systems serving Wisconsin?
Wisconsin has 3,023 EPA violations on record across 466 ZIP codes; 766 are classified as health-based violations. The remainder are monitoring or reporting violations.
Which city in Wisconsin has the worst water quality?
Waukesha, WI has the most recorded EPA violations (144) among the cities with mapped water systems in Wisconsin in our data. Check your water supplier's report and test your tap water for the most accurate picture of your local water quality.
Which city in Wisconsin has the best water quality?
Violation records vary by water system across Wisconsin. Check individual city reports for details.
What contaminants are found in Wisconsin drinking water?
EPA regulates over 90 drinking-water contaminants nationally; water systems in Wisconsin monitor those applicable to each system, which can include lead, copper, nitrate, disinfection byproducts, and bacteria. The most common violations vary by region - check your ZIP code for contaminant-specific data.