Montana Water Quality Report: 2,102 Violations Across 405 ZIPs
623 water systems · 405 ZIP codes · 2,102 violations · Updated 2026-05-31
Data: EPA Safe Drinking Water Information System (SDWIS), EPA ECHO Last verified: 2026-05-31
City Water Quality Map: Montana
Each circle represents a city. Size indicates population, color indicates water quality grade. Tap a circle for details.
Violation Trend
EPA violations across all water systems in Montana.
Cities with Most Violations in Montana
| # | City | Grade | Violations | Systems | Population | |
|---|---|---|---|---|---|---|
| 1 | Billings | C | 476 | 5 | 133,600 | Details → |
| 2 | Helena | F | 288 | 5 | 36,935 | Details → |
| 3 | Great Falls | C | 65 | 5 | 72,250 | Details → |
| 4 | Ashland | F | 62 | 2 | 1,050 | Details → |
| 5 | Denton | D | 61 | 1 | 255 | Details → |
| 6 | Glasgow | F | 42 | 3 | 3,883 | Details → |
| 7 | Butte | C | 40 | 2 | 33,090 | Details → |
| 8 | Fort Smith | D | 36 | 3 | 1,325 | Details → |
| 9 | Harlem | D | 31 | 2 | 862 | Details → |
| 10 | Wolf Creek | F | 29 | 1 | 67 | Details → |
Most Common Contaminants in Montana
| Contaminant | Category | Violations | ZIPs Affected | Health Risk |
|---|---|---|---|---|
| Surface Water Treatment Rule | Treatment Technique | 462 | 142 | No |
| Stage 1 DBP Rule | Treatment Technique | 372 | 134 | Yes |
| Contaminant 0700 | Other | 283 | 43 | Yes |
| Total Trihalomethanes (TTHM) | Disinfection Byproducts | 241 | 92 | Yes |
| Arsenic | Inorganic | 138 | 67 | Yes |
| E. coli | Microbiological | 61 | 13 | Yes |
| Haloacetic Acids (HAA5) | Disinfection Byproducts | 54 | 6 | Yes |
| Contaminant 0800 | Other | 50 | 5 | Yes |
| Total Coliform | Microbiological | 47 | 35 | No |
| Combined Radium | Radionuclides | 18 | 1 | Yes |
Water Quality Overview
Montana has 623 community water systems serving approximately 1,254,766 people across 405 ZIP codes. These systems have accumulated 2,102 EPA violations, including 431 health-based violations.
Health-based violations account for 21% of all violations in Montana. 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 | 431 | 20.5% |
| Monitoring/Reporting | 1,671 | 79.5% |
| Total | 2,102 | 100% |
Health-based violations indicate contaminant levels exceeding EPA Maximum Contaminant Levels (MCLs). 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 Montana have the highest number of EPA violations:
| Rank | City | Grade | Violations | Water Systems | Population |
|---|---|---|---|---|---|
| 1 | Billings | C | 476 | 5 | 133,600 |
| 2 | Helena | F | 288 | 5 | 36,935 |
| 3 | Great Falls | C | 65 | 5 | 72,250 |
| 4 | Ashland | F | 62 | 2 | 1,050 |
| 5 | Denton | D | 61 | 1 | 255 |
| 6 | Glasgow | F | 42 | 3 | 3,883 |
| 7 | Butte | C | 40 | 2 | 33,090 |
| 8 | Fort Smith | D | 36 | 3 | 1,325 |
| 9 | Harlem | D | 31 | 2 | 862 |
| 10 | Wolf Creek | F | 29 | 1 | 67 |
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 Montana:
| Year | Total Violations | Health-Based |
|---|---|---|
| 2021 | 43 | 43 |
| 2022 | 116 | 116 |
| 2023 | 93 | 93 |
| 2024 | 85 | 85 |
| 2025 | 132 | 132 |
| 2026 | 15 | 15 |
Violations have decreased from 43 in 2021 to 15 in 2026, suggesting improving compliance across Montana.
Most Common Contaminants
The following contaminants have caused the most violations across Montana water systems:
| Contaminant | Category | Violations | ZIPs Affected | Health-Based |
|---|---|---|---|---|
| Surface Water Treatment Rule | Treatment Technique | 462 | 142 | No |
| Stage 1 DBP Rule | Treatment Technique | 372 | 134 | Yes |
| Total Trihalomethanes (TTHM) | Disinfection Byproducts | 241 | 92 | Yes |
| Arsenic | Inorganic | 138 | 67 | Yes |
| E. coli | Microbiological | 61 | 13 | Yes |
| Haloacetic Acids (HAA5) | Disinfection Byproducts | 54 | 6 | Yes |
| Total Coliform | Microbiological | 47 | 35 | No |
| Combined Radium | Radionuclides | 18 | 1 | Yes |
| Barium | Inorganic | 12 | 7 | Yes |
| Nickel | Inorganic | 11 | 4 | No |
How to Check Your Water in Montana
Enter your ZIP code on ZipCheckup for detailed water system data including contaminant levels, violation history, and safety scores
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 2,879 enforcement actions against water systems in Montana. 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 mean a contaminant was detected above the EPA's Maximum Contaminant Level (MCL) — the legal limit designed to protect human health. Montana has 431 such violations across its water systems. Not all violations cause illness, but repeated exceedances increase risk, especially for children and immunocompromised individuals.
Understanding water quality grades
ZipCheckup grades water systems from A to F based on EPA violation history, contaminant levels, and system compliance. Grade A means few or no violations; Grade F indicates persistent or serious 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 Montana?
Montana has 623 community water systems with 2,102 recorded EPA violations, including 431 health-based. Water quality varies by city and ZIP code — check your specific location for detailed results.
How many water violations does Montana have?
Montana has 2,102 total EPA violations across 405 ZIP codes. 431 are health-based violations that indicate contaminant levels potentially harmful to human health. The remainder are monitoring or reporting violations.
Which city in Montana has the worst water quality?
Billings, MT has the most EPA violations among major cities in Montana with 476 recorded violations. Check individual ZIP codes for the most accurate picture of your local water quality.
Which city in Montana has the best water quality?
Several cities in Montana maintain excellent EPA compliance. Check individual city reports for details.
What contaminants are found in Montana drinking water?
Montana water systems are monitored for over 90 EPA-regulated contaminants including lead, copper, nitrates, disinfection byproducts, and bacteria. The most common violations vary by region — check your ZIP code for contaminant-specific data.