Montana Water Quality Deep Dive - 1,958 Systems Analyzed

Executive Summary

Montana operates 1,958 public water systems monitored through state and federal testing programs, serving communities across 293 ZIP codes. Our analysis of 7,307 individual test results from EPA, state laboratory data, and Consumer Confidence Reports reveals 133 instances where contaminant levels exceeded federal or state Maximum Contaminant Levels (MCLs) - an overall exceedance rate of 1.82%.

The state's primary water quality challenges center on mining legacy contamination and naturally occurring arsenic in western Montana groundwater. Geographic risk patterns across Montana reflect mining legacy contamination including the Butte/Anaconda Superfund complex (one of the largest in the nation), naturally occurring arsenic in western Montana groundwater, and PFAS from military installations.

This report is not a summary - it is a ground-level examination of what the data actually shows. Every number comes from EPA SDWIS enforcement records, state laboratory testing programs, Consumer Confidence Reports filed by utilities, FEMA flood insurance claims, and Census Bureau housing stock data. Where the data tells a clear story, we state it plainly. Where it is ambiguous or incomplete, we note that too.

Contaminant Analysis

State laboratory testing and EPA monitoring data reveal the scope of contamination across Montana's water supply. The following analysis covers both regulated contaminants with federal MCLs and state-specific standards - Montana follows federal MCLs; DEQ manages the complex mining legacy cleanup while balancing oversight of small rural systems.

Top Contaminants by MCL Exceedance Rate

How to read the copper row. EPA's federal reporting schema defines the CU90 code as a Copper Action Level Exceedance: the record exists only where a system's 90th-percentile copper result was at or above the 1.3 mg/L action level. Every copper record in this dataset is therefore an exceedance, which is why no rate is shown - there is no denominator of clean copper results to compute one from. For the same reason, a system with no copper record has not been shown to be clean: non-exceedance copper results are optional to report for systems serving 3,300 people or fewer. We do not publish a copper level because the same schema transmits no verified unit of measure for this code.

Copper appears here differently from every other contaminant in the table. EPA's federal database records a copper 90th-percentile result under the CU90 code specifically when it exceeds the 1.3 mg/L action level, so Montana's 62 copper records across 36 systems are 62 action-level exceedances, not a sample of routine copper testing. Copper leaches from the same plumbing that leaches lead - household pipes, solder and fixtures - and the corrosion control that keeps one in check is what keeps the other in check. Read the count, not a rate: there is no reported population of clean copper results to divide by, and a system missing from this line has not been shown to be clean, only to have reported nothing.

PFAS ("Forever Chemicals") in Montana

PFAS monitoring in Montana covers 1,792 individual tests across multiple PFAS compounds. Current testing shows no exceedances of the 2024 EPA PFAS MCLs, though monitoring is ongoing and detection does not require exceedance to pose health concerns.

State vs. Federal Standards

Montana follows federal MCLs; DEQ manages the complex mining legacy cleanup while balancing oversight of small rural systems.

This regulatory landscape creates a two-tier compliance reality. A water system in Montana may appear "in compliance" on federal reports while actually exceeding stricter state limits. For residents reading their annual Consumer Confidence Report, this distinction matters enormously - the report may reference federal standards while the state is enforcing tighter ones.

The gap between state and federal standards also affects how violations are counted. Our dataset captures both tiers, which is why the exceedance counts above may differ from EPA-only reporting. When we say a system "exceeds the MCL," we mean the applicable limit - federal or state, whichever is stricter.

Worst Water Systems by Violations

The following systems had the highest number of MCL exceedances in our dataset. A critical caveat: exceedance count alone does not mean a system is currently unsafe. Many exceedances are resolved through treatment adjustments, blending, or switching water sources. However, patterns of repeated violations across multiple contaminants or multiple years indicate systemic issues - underfunding, aging treatment infrastructure, or management failures - that are unlikely to resolve without intervention.

PALISADES APARTMENTS leads with 8 exceedances in our dataset. PWSID MT0001542 follows with 7 exceedances.

If you receive water from any of these systems, we recommend checking your specific ZIP code report for the most current violation status and filtration recommendations. Exceedance data tells you what has happened - your ZIP report tells you what to do about it.

Of Montana's 1,958 monitored systems, the top 10 worst offenders account for 44 of the state's 133 total exceedances. This concentration pattern is common - a small number of chronically non-compliant systems drive a disproportionate share of violations statewide.

Enforcement & Compliance

EPA and state enforcement actions tell the story of how violations translate (or fail to translate) into accountability. The enforcement pipeline works in stages: a violation is detected, an informal action (like a warning letter) may be issued, and if non-compliance persists, formal enforcement - consent orders, administrative orders, or court actions - follows. The ratio between informal and formal actions reveals how aggressively a state pursues compliance.

Only 0% of enforcement actions in Montana are formal (court orders, consent decrees, administrative penalties). The remaining 100% are informal - warning letters, compliance schedules, and technical assistance. This ratio matters: informal actions carry no legal penalty and rely on voluntary compliance. When systems repeatedly violate MCLs without facing formal enforcement, the deterrent effect weakens.

181 violations remain officially unresolved across the state. Each unresolved violation represents a system where contamination was detected, documented, and - as of our latest data - not yet remediated to the satisfaction of regulators. Berkeley Pit cleanup and Milltown Dam removal represent landmark mining remediation; arsenic compliance in small groundwater systems remains an ongoing challenge.

Areas with Most Health Violations

Geographic Risk Patterns

Water quality risk in Montana is not evenly distributed. Mining legacy contamination including the Butte/Anaconda Superfund complex (one of the largest in the nation), naturally occurring arsenic in western Montana groundwater, and PFAS from military installations create distinct regional patterns that are visible in the data.

Understanding where water quality problems concentrate is as important as understanding what contaminants are present. A statewide average conceals enormous ZIP-to-ZIP variation - two communities 20 miles apart may have completely different risk profiles based on their water source, treatment infrastructure, and local geology.

Data Anomalies & Notable Findings

Our automated anomaly detection system flagged 8+ patterns worth investigation in Montana:

High-severity findings:

• ZIP 59241 (severity 9/10): Children in Hinsdale, MT (59241) attend school in a lead-risk zone with 1952-era plumbing - View full report
• ZIP 59247 (severity 9/10): Children in Medicine Lake, MT (59247) attend school in a lead-risk zone with 1966-era plumbing - View full report
• ZIP 59454 (severity 9/10): Children in Kevin, MT (59454) attend school in a lead-risk zone with 1952-era plumbing - View full report

Lead Exposure & Infrastructure Age

Lead contamination in drinking water is almost never caused by the water source itself - it leaches from lead service lines, lead solder in copper pipes, and brass fixtures as water sits in contact with these materials. This means lead risk is fundamentally an infrastructure problem, and infrastructure age is the single strongest predictor.

In Montana, Vast distances and sparse population make water system maintenance and oversight challenging; many small systems serve remote communities with limited technical capacity. The federal Lead and Copper Rule (LCR) requires utilities to test a sample of high-risk homes and report the 90th percentile lead level - meaning 90% of samples must be below the 15 ppb action level. But this sampling methodology has long been criticized: utilities often avoid the worst homes, and the action level itself is not a health-based standard (the EPA has stated there is no safe level of lead exposure).

Across Montana, 194 ZIP codes have elevated or high lead pipe risk based on housing age, and 95 have elevated electrical system risk. These infrastructure age indicators are derived from Census Bureau American Community Survey data on housing stock vintage.

The connection between housing age and water contamination risk is well-documented: homes built before 1986 (when the federal ban on lead solder took effect) are significantly more likely to have lead in their plumbing. Homes built before 1950 face even higher risk, as lead service lines were standard construction practice in many parts of the country during that era.

Highest Lead Exposure Risk ZIP Codes

Flood Risk & Water Infrastructure

Flooding directly threatens water quality through multiple mechanisms: overwhelmed treatment plants release partially treated water, floodwaters can infiltrate well heads and contaminate groundwater sources, damaged distribution lines create entry points for bacteria and sediment, and power outages disable treatment systems entirely. In the aftermath of major flood events, boil-water advisories become common - but many residents in affected areas may not receive timely notification.

• 131 ZIP codes in Montana have FEMA flood insurance claims on record
• 2,037 total flood insurance claims filed historically
• $17.5 million in total flood damage payouts

The average flood insurance claim payout in Montana is $8,575. While flood damage is typically associated with structural property damage, the water quality implications are often overlooked. Communities with repeated flooding face compounding infrastructure degradation - each event weakens pipes, treatment facilities, and distribution systems that may not be fully restored before the next event.

Consumer Confidence Reports (CCRs)

Water utilities are required to publish annual Consumer Confidence Reports. We have parsed CCR data for 292 ZIP codes in Montana, documenting 362 self-reported violations and 218 systems with detectable lead levels.

CCR data is self-reported by utilities and may undercount actual contamination events. Cross-referencing CCR data with EPA SDWIS violation records provides a more complete picture - which is exactly what ZipCheckup reports do for every ZIP code.

Trend Analysis & Regulatory Outlook

Berkeley Pit cleanup and Milltown Dam removal represent landmark mining remediation; arsenic compliance in small groundwater systems remains an ongoing challenge.

Three major regulatory forces are reshaping water quality across Montana and the country:

Lead and Copper Rule Improvements (LCRI): The 2024 LCRI represents the most significant update to lead regulation since the original 1991 rule. It requires all water systems to complete a lead service line inventory, lower the action level trigger from 15 ppb to 10 ppb, and replace all lead service lines within 10 years. For Montana's 1,958 systems, this means billions in infrastructure investment - and a fundamental reshaping of the lead risk landscape we document above.

PFAS National Primary Drinking Water Regulation (2024): For the first time, EPA set enforceable MCLs for six PFAS compounds - PFOA and PFOS at 4 ppt, and four others at various levels. Systems nationwide are still in the initial monitoring phase, which is why our PFAS data captures detections that may not yet have triggered formal violations. Treatment to remove PFAS (primarily granular activated carbon or reverse osmosis) is expensive, and many small systems will struggle to comply within the 3–5 year implementation timeline.

State-level action: Montana follows federal MCLs; DEQ manages the complex mining legacy cleanup while balancing oversight of small rural systems. As federal regulation catches up to state standards in some areas, the patchwork of requirements creates an uneven compliance landscape that makes cross-state comparisons complex but ZIP-level analysis essential.

What Montana Residents Should Do

Based on our analysis of 7,307 test results and 293 ZIP codes, here are specific actions for Montana residents:

1. Check your ZIP code report - enter your ZIP at ZipCheckup.com to see contaminant data, violation history, and risk scores specific to your address
2. Request your utility's CCR - if your ZIP is not in our CCR database, request the latest Consumer Confidence Report directly from your water utility
3. Test your water independently - home water testing kits ($30–$150) can detect lead, bacteria, and common contaminants. Lab testing ($100–$400) provides more comprehensive results
4. Consider filtration - for the contaminants most prevalent in Montana (Arsenic, Lead, Nitrate), reverse osmosis or NSF-certified carbon filters provide the most effective protection
5. Check for lead service lines - if your home was built before 1986, contact your utility to determine if you have a lead service line. Many utilities now offer free inspections
6. Prepare for flood events - if you're in a flood-prone area, keep bottled water reserves and know how to shut off your water main. After any flood, do not use tap water until your utility confirms safety

Methodology & Data Sources

This analysis combines multiple data sources:

• EPA SDWIS - Safe Drinking Water Information System violation and enforcement records
• State laboratory data - MT — Lead & Copper 90th Percentile (EPA ECHO LCR); MT — PFAS Monitoring (UCMR5 National Dataset); MT — SDWIS Health-Based Violations (EPA Envirofacts); MT — Community Water Systems (EPA SDWIS) (7,307 records)
• EPA ECHO - Enforcement and Compliance History Online, including PFAS detections and enforcement actions
• Consumer Confidence Reports - parsed and cross-referenced with EPA data for 292 ZIP codes
• FEMA NFIP - National Flood Insurance Program claims data
• Census ACS - Housing age and demographic data for infrastructure risk modeling
• Lead exposure modeling - ZipCheckup's proprietary lead risk score combining housing age, water test results, and service line data

All data is updated regularly. This report reflects data available as of 2026-07-19.

Related Reports

• Montana State Overview - ZIP rankings, county breakdown, and safety scores
• Water Safety Rankings by State - compare Montana to other states

Highest-Risk ZIP Codes in Montana

• 59241 Hinsdale Water Report - Lead: 29 ppb
• 59484 Sweet Grass Water Report - Lead: 15 ppb
• 59454 Kevin Water Report - Lead: 12 ppb
• 59756 Warm Springs Water Report - Lead: 2 ppb
• 88421 Water Report

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  author = {{ZipCheckup}},
  title  = {{Montana Water Quality Deep Dive - 1,958 Systems Analyzed}},
  year   = {2026},
  url    = {https://zipcheckup.com/states/montana/deep-dive/}
}