Idaho Water Quality Report: 2,266 Water-System Violations Mapped to 107 ZIPs
206 water systems · 107 ZIP codes · 2,266 violations
Data: EPA Safe Drinking Water Information System (SDWIS), EPA ECHO
ZipCheckup tracks EPA drinking-water compliance for 206 public water systems serving 107 ZIP codes in Idaho. The state record shows 2,266 EPA violations, 127 health-based.
City Water Quality Map: Idaho
Each circle represents a city. Size indicates population, color indicates water quality grade. Tap a circle for details.
Cities with Most Violations in Idaho
| # | City | Grade | Violations | Systems | Population | |
|---|---|---|---|---|---|---|
| 1 | Mountain Home | 149 | 1 | 22,580 | Details → | |
| 2 | Glenns Ferry | 149 | 1 | 1,637 | Details → | |
| 3 | Boise | 139 | 13 | 265,704 | Details → | |
| 4 | Rexburg | 138 | 3 | 50,704 | Details → | |
| 5 | Garden City | 127 | 5 | 26,989 | Details → | |
| 6 | Mountain Home A F B | 111 | 1 | 3,198 | Details → | |
| 7 | Blackfoot | 93 | 2 | 29,244 | Details → | |
| 8 | Firth | 91 | 2 | 1,929 | Details → | |
| 9 | Mccall | 73 | 2 | 7,507 | Details → | |
| 10 | Idaho Falls | 66 | 6 | 122,947 | Details → |
Most Common Contaminants in Idaho
| Contaminant | Category | Violations | ZIPs Affected | Health Risk |
|---|---|---|---|---|
| Lead and Copper Rule | Treatment Technique | 73 | 37 | Yes |
| Chlorine | Disinfectant | 71 | 35 | No |
| Nitrate | Inorganic | 59 | 26 | Yes |
| Lead and Copper Rule Revisions | Treatment Technique | 54 | 31 | Yes |
| Oxamyl (Vydate) | Organic | 53 | 26 | No |
| Carbofuran | Organic | 53 | 26 | No |
| Endothall | Organic | 51 | 23 | No |
| 2,4,5-TP (Silvex) | Organic | 50 | 23 | No |
| Endrin | Organic | 49 | 23 | No |
| BHC-gamma (Lindane) | Organic | 49 | 23 | No |
Water Quality Overview
Idaho has 206 community water systems represented across 107 directly mapped ZIP records. The associated city records cover approximately 1,706,175 people. The available records contain 2,266 EPA violations, including 127 health-based violations.
Health-based violations account for 6% of all violations in Idaho. 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 | 127 | 5.6% |
| Monitoring/Reporting | 2,139 | 94.4% |
| Total | 2,266 | 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 Idaho have the highest number of EPA violations:
| Rank | City | Violations | Water Systems | Population |
|---|---|---|---|---|
| 1 | Mountain Home | 149 | 1 | 22,580 |
| 2 | Glenns Ferry | 149 | 1 | 1,637 |
| 3 | Boise | 139 | 13 | 265,704 |
| 4 | Rexburg | 138 | 3 | 50,704 |
| 5 | Garden City | 127 | 5 | 26,989 |
| 6 | Mountain Home A F B | 111 | 1 | 3,198 |
| 7 | Blackfoot | 93 | 2 | 29,244 |
| 8 | Firth | 91 | 2 | 1,929 |
| 9 | Mccall | 73 | 2 | 7,507 |
| 10 | Idaho Falls | 66 | 6 | 122,947 |
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 Idaho:
| Year | Health-based violations |
|---|---|
| 2021 | 18 |
| 2022 | 14 |
| 2023 | 18 |
| 2024 | 31 |
| 2025 | 13 |
| 2026 | 3 |
Health-based violations have decreased from 18 in 2021 to 3 in 2026, suggesting improving compliance across Idaho.
Most Common Contaminants
The following contaminants have caused the most violations across Idaho water systems:
| Contaminant | Category | Violations | ZIPs Affected | Health-Based |
|---|---|---|---|---|
| Lead and Copper Rule | Treatment Technique | 73 | 37 | Yes |
| Chlorine | Disinfectant | 71 | 35 | No |
| Nitrate | Inorganic | 59 | 26 | Yes |
| Lead and Copper Rule Revisions | Treatment Technique | 54 | 31 | Yes |
| Atrazine | Organic | 49 | 23 | No |
| Di(2-ethylhexyl) phthalate | Organic | 48 | 23 | No |
| Combined Uranium | Radionuclides | 48 | 19 | Yes |
| Public Notice Rule | Reporting | 44 | 17 | No |
| Haloacetic Acids (HAA5) | Disinfection Byproducts | 43 | 23 | Yes |
| Gross Alpha (excl. radon and uranium) | Radionuclides | 26 | 14 | No |
How to Check Your Water in Idaho
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 Idaho. 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. Idaho has 127 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 Idaho?
Records for 206 community water systems mapped to ZIPs in Idaho show 2,266 reported violations, including 127 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 Idaho?
Idaho has 2,266 EPA violations on record across 107 ZIP codes; 127 are classified as health-based violations. The remainder are monitoring or reporting violations.
Which city in Idaho has the worst water quality?
Mountain Home, ID has the most recorded EPA violations (149) among the cities with mapped water systems in Idaho 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 Idaho has the best water quality?
Violation records vary by water system across Idaho. Check individual city reports for details.
What contaminants are found in Idaho drinking water?
EPA regulates over 90 drinking-water contaminants nationally; water systems in Idaho 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.