Data: EPA Safe Drinking Water Information System (SDWIS) Last verified: 2026-05-03

SDWIS records for Thompson Falls, MT show 4 EPA violations documented for the local water supply — these span the full range of reportable events from health-based exceedances to monitoring and reporting lapses registered with the federal program.

Water Quality by ZIP Code in Thompson Falls

Water quality varies across Thompson Falls's 1 ZIP codes. Check your specific ZIP for detailed contaminant data.

ZIP Code	Grade	Score	Violations	Health
59873	C	64	4	0	View report →

Water Quality Overview

Thompson Falls, Montana receives a water quality grade of C with an overall score of 64 out of 100, based on EPA compliance data from the Safe Drinking Water Information System (SDWIS).

The 4 water systems serving Thompson Falls have accumulated 4 EPA violations (all monitoring/reporting type). These violations are tracked across 1 ZIP codes serving approximately 2,345 people.

What Grade C Means

A grade of C indicates moderate compliance issues. Thompson Falls's water systems have some violations that warrant attention. While the water may still be safe for most people, residents in affected ZIP codes should consider additional testing or filtration.

Lead Levels

The average 90th percentile lead level across Thompson Falls water systems is 0.0010 mg/L — within EPA limits. No ZIP codes exceed the EPA lead action level.

With 56% of homes built before 1986, Thompson Falls has a higher-than-average risk of lead from older plumbing. Lead solder was banned in 1986, and homes built before this date may have lead in pipes, solder joints, or fixtures.

Radon Risk

Thompson Falls is in EPA Radon Zone 1 (High risk). The EPA recommends all homes in Zone 1 areas be tested for radon. Radon is the second leading cause of lung cancer after smoking.

Water Systems Serving Thompson Falls

Thompson Falls is served by 4 community water systems regulated under the Safe Drinking Water Act. These systems collectively serve approximately 2,345 people across 1 ZIP codes.

Each water system is identified by a Public Water System ID (PWSID) and is required to:

• Test for over 90 regulated contaminants on a regular schedule
• Report results to the EPA and state regulators
• Issue an annual Consumer Confidence Report (CCR) to all customers
• Take corrective action when violations occur

The EPA has taken 10 enforcement actions against water systems serving Thompson Falls. Enforcement actions range from informal compliance assistance to formal orders and penalties.

How to Check Your Water in Thompson Falls

1. Enter your ZIP code on ZipCheckup to see your specific water system data, including contaminant levels, violation history, and safety scores

2. Request your CCR — your water utility must provide an annual Consumer Confidence Report with detailed test results for all monitored contaminants

3. Get a home test — certified kits cost $20–$50 and test for lead, bacteria, and common contaminants. Professional lab tests ($150–$400) cover a broader panel

4. Consider filtration — NSF-certified filters can remove specific contaminants. Reverse osmosis removes the broadest range; activated carbon is effective for chlorine and many organics

5. Check for advisories — monitor your local utility website and local news for boil water advisories or system alerts

Contaminants Detected in Thompson Falls Water Systems

The following contaminants have been detected or caused violations across Thompson Falls's water systems:

MCL = Maximum Contaminant Level (EPA enforceable standard). Health-based violations indicate levels that may pose direct health risks.

EPA Enforcement History

The EPA and state regulators have taken 10 enforcement actions against water systems serving Thompson Falls. Recent actions:

Enforcement actions range from informal compliance assistance to formal orders and penalties. The most recent action was on 2025-01-16.

Thompson Falls vs. Nearby Montana Cities

How Thompson Falls's water quality compares to similar cities in Montana:

Common Questions About Thompson Falls Water

These are the most common questions residents search for about water quality in Thompson Falls, Montana:

Is Thompson Falls water hard or soft? Water hardness varies by source. Thompson Falls's 4 water systems use multiple sources. Check your ZIP code report for specific hardness data.

Can I drink Thompson Falls tap water? Thompson Falls's water receives a grade of C (64/100). No health-based violations have been recorded, but home testing is always recommended.

What is the best water filter for Thompson Falls? A NSF/ANSI 53-certified filter for lead removal is a good general choice. See our Water Filter Matcher for personalized recommendations.

Thompson Falls vs. Montana Average

Understanding how Thompson Falls compares to the broader Montana average helps contextualize your local water quality. Factors like water source, treatment methods, and infrastructure age all contribute to differences between cities in the same state.

To see how individual neighborhoods compare, check the ZIP code reports below — water quality can vary significantly even within Thompson Falls.

ZIP Codes in Thompson Falls

Thompson Falls spans 1 ZIP code. The ZIP with the lowest water quality score is 59873. Each ZIP code has its own water quality profile based on the specific water system serving that area. Check each ZIP code for detailed contaminant data, violation history, and system information.

Data Sources

• Water quality: EPA Safe Drinking Water Information System (SDWIS)
• Lead/copper: EPA Lead and Copper Rule sampling data
• Radon: EPA Map of Radon Zones
• Enforcement: EPA ECHO database
• Filter recommendations: NSF/ANSI certified products

Updated daily.