PFAS in Montana drinking water

5 drinking-water utilities in Montana reported PFAS detections at or above the EPA minimum reporting level under UCMR 5 (the federal monitoring round that ran 2023–2025). Of those, 2 exceeded the final EPA Maximum Contaminant Level for PFOA or PFOS (4 parts per trillion), serving roughly 20,133 people.

By the numbers

• 5 Montana water utilities with at least one PFAS compound detected
• 37,615 people served by those utilities
• 2 utilities above the final 4 ppt MCL for PFOA or PFOS
• 4 federal and Department of Defense sites with reported PFAS in groundwater

The interactive map below plots every reporting Montana utility, colour-coded by whether their worst reading exceeds the federal MCL, sits below it but at or above the reporting threshold, or falls below the reporting threshold. Use the search box to find a specific utility, ZIP code or address.

Top Montana water utilities by PFAS impact

The 15 Montana public water systems with the most significant PFAS detections under UCMR 5, ranked by how far each system’s worst MCL-exceeding compound runs over the federal limit:

Use the interactive map above to find every utility (not just the top 15) and to search by ZIP code or address.

The biggest Montana systems above the PFOA/PFOS MCL

Ranked by population served, the largest Montana water utilities reporting at least one PFAS reading above EPA’s final MCL:

PFAS compounds detected in Montana

UCMR 5 required utilities to test for 29 different PFAS compounds. The table below shows how many Montana utilities had at least one above-reporting-level result for each compound, sorted by frequency:

Where Montana’s PFAS contamination is coming from

EPA’s PFAS Analytic Tools also catalogue the suspected industrial, federal and accidental sources of PFAS in each state. Montana has 4 federal facilities (mostly U.S. military installations and federal airports) reporting PFAS in groundwater, 0 EPA Superfund sites flagged for PFAS, and 1 recorded PFAS-related spill (1 of which reached surface water).

Federal and DoD sites with the highest PFAS in groundwater

The U.S. Department of Defense has reported PFAS contamination at hundreds of installations nationwide, largely tied to decades of fire-training exercises with PFAS-based firefighting foams (AFFF). These readings are taken from monitoring wells at the source site, not from drinking-water taps, but plumes from these sites are a known route into nearby public and private water supplies. Readings are in parts per trillion (ppt) of PFOS and PFOA respectively:

What “exceeds the MCL” means here

In April 2024 the EPA finalised the first-ever federal Maximum Contaminant Levels (MCLs) for six PFAS compounds in drinking water. The two most consequential are PFOA and PFOS, both set at 4.0 nanograms per litre (ng/L) — equivalent to 4 parts per trillion. Every red marker on the map above represents a Montana water system whose most-recent UCMR 5 result for PFOA or PFOS sat above 4 ng/L.

EPA also issued individual MCLs of 10 ng/L for PFHxS, PFNA and HFPO-DA (GenX) and a Hazard-Index MCL covering mixtures. In May 2025 the agency confirmed the PFOA and PFOS limits would stay in place (with the compliance deadline extended to 2031), and announced its intent to rescind the four other limits. We continue to flag exceedances of the published April 2024 MCL for those compounds and label them as “under EPA reconsideration” so the rule status is honest and current.

Yellow markers mean PFAS were detected at or above EPA’s reporting threshold (the minimum reporting level) but no individual compound exceeded an MCL. Detection at any level is not necessarily a regulatory violation, but it is a signal that PFAS treatment may be needed before the 2031 compliance deadline.

Methodology and data sources

• Drinking-water detections: EPA PFAS Analytic Tools, UCMR 5 layer. Filtered to Montana samples at or above the minimum reporting level. We aggregate the raw 2023–2025 sample records to one entry per public water system, taking the most-recent reading per compound.
• Superfund sites: EPA PFAS Analytic Tools, Superfund-with-PFAS layer. Includes National Priorities List sites and Superfund Alternative Approach sites where PFAS has been detected.
• Federal and DoD sites: EPA PFAS Analytic Tools, federal-sites layer. PFOA and PFOS values are maximum readings from groundwater monitoring wells at each installation, not finished drinking water.
• Spills: EPA PFAS Analytic Tools, spills layer. Covers reported releases involving PFAS-containing materials.

UCMR 5 only required community water systems serving 3,300 or more people, plus a representative sample of smaller systems, to test for PFAS. Private wells, very small public systems, and bottled water are not in this dataset. Absence of a dot on the map does not mean absence of PFAS.

What you can do

• Check whether your utility appears in the table above or on the map. If it does, your utility is required to come into compliance with the federal PFOA/PFOS MCL by 2031 — usually via granular activated carbon, ion-exchange resin or reverse osmosis treatment.
• If you are on a private well in or near a flagged area, consider independent PFAS testing through a state-certified laboratory.
• Look up your most recent Consumer Confidence Report (CCR), which utilities are required to publish annually. PFAS results from UCMR 5 must now appear there.
• If you want point-of-use protection, only filters certified to NSF/ANSI 53 or NSF/ANSI 58 for PFOA and PFOS reduction will reliably remove PFAS.

Related

• National PFAS contamination map (all 50 states)
• US Superfund sites map
• EPA PFAS Analytic Tools (raw data)
• EPA PFAS National Primary Drinking Water Regulation