Free Montana water report: PFAS & lead levels for every water system, worst-affected cities, and EPA violations. Check your ZIP.
Montana's drinking water serves approximately 1.1 million residents across the fourth-largest state by area – a landscape that ranges from the Rocky Mountain front in the west to the Great Plains in the east. The state's water sources are as varied as its geography: mountain communities draw from snowmelt-fed rivers and alpine aquifers, while eastern Montana relies on the Missouri and Yellowstone river systems and deep sedimentary aquifers. The Montana Department of Environmental Quality (DEQ) regulates about 2,100 public water systems, most of them small. Billings, the largest city at roughly 120,000 people, draws from the Yellowstone River. Great Falls uses the Missouri River. Missoula sits atop one of the largest and cleanest alluvial aquifers in the northern Rockies.
Montana's water is, in many places, exceptional. Mountain source water – cold, low in dissolved minerals, and distant from major industrial activity – produces some of the cleanest drinking water in the country. But Montana also carries the legacy of a mining industry that extracted gold, silver, copper, and other metals for over a century, leaving contamination that persists to this day.
PFAS contamination in Montana is centered on one site: Malmstrom Air Force Base in Great Falls. The base, home to the 341st Missile Wing and its fleet of Minuteman III ICBMs, has used AFFF in firefighting training over many decades. PFAS has been detected in groundwater on and around the base, with some monitoring wells showing concentrations well above federal health advisory levels.
The contamination has raised concerns for Great Falls residents, particularly those in neighborhoods near the base that may draw from affected groundwater. The city's municipal supply comes from the Missouri River, which is upstream of the primary contamination zone, but private wells and some smaller systems in the area may be exposed.
Beyond Malmstrom, Montana's PFAS data is sparse. The UCMR5 program is providing initial results for larger public water systems, but the state's many small systems and extensive private well use mean most of Montana is untested. Montana DEQ has not adopted state-specific PFAS MCLs and relies on federal standards.
Montana's clean mountain water – the headwaters of the Columbia, Missouri, and Yellowstone river systems all originate in the state – means that most communities face minimal PFAS risk from ambient contamination. The concern is localized around point sources: military bases, airports, and fire training facilities.
Among Rocky Mountain states, Montana has a less severe PFAS profile than Colorado (which has multiple military bases and the Peterson/Schriever contamination) or New Mexico (which has Cannon and Holloman AFB sites). Wyoming, Idaho, and the Dakotas have similarly limited PFAS data.
Montana's distinctive water quality challenge is mining legacy contamination. The Berkeley Pit in Butte – a former open-pit copper mine now filled with over 40 billion gallons of acidic, metal-laden water – is one of the largest Superfund sites in the country. The Clark Fork River, which flows from Butte through Missoula and into the Columbia River system, was contaminated by over a century of copper smelting operations run by the Anaconda Copper Mining Company. The Clark Fork River Superfund complex stretches over 120 miles and is the largest Superfund site by area in the United States.
Arsen, cadmium, copper, lead, and zinc from mining tailings and smelter slag contaminated floodplain soils and sediments throughout the upper Clark Fork watershed. Remediation has been ongoing since the 1980s, and while water quality has improved significantly, the mining legacy remains measurable in sediment and soil throughout the watershed.
For most Montanans, water quality is not a daily concern – the state's water is genuinely clean in most locations. But specific risks exist depending on where you live.
1. Check your location at the homepage. We show available data by ZIP code, including any PFAS results. 2. Great Falls area residents near Malmstrom AFB should verify their water source. If you are on a private well within several miles of the base, consider PFAS testing. 3. Upper Clark Fork watershed residents (Butte, Anaconda, Deer Lodge, Missoula) should be aware of mining legacy metals in soil and potentially in older well infrastructure. Municipal systems in these areas are treated and monitored, but private wells may not be. 4. Review our water filter guide for options appropriate to your situation. A detailed water report provides context specific to your address.
Montana's water history is a tale of two economies: mining and agriculture, each leaving distinct marks on the landscape.
The copper mining era in Butte and Anaconda – spanning roughly 1880 to 1980 – made Montana one of the wealthiest states in the union for a time and one of the most environmentally damaged. The Anaconda Company's smelter in Anaconda processed millions of tons of copper ore, releasing arsenic and heavy metals across the landscape. When the Berkeley Pit was closed in 1982 and its groundwater pumps turned off, the pit began filling with contaminated water that is now one of the most toxic bodies of water in North America. The EPA has been managing the site since its Superfund listing in 1983, and treatment of pit water to prevent it from reaching Butte's alluvial aquifer is an ongoing, indefinite operation.
Malmstrom AFB has been operational since 1942, initially as an Army Air Corps training base and later as a strategic missile installation. The base's PFAS contamination follows the standard pattern: firefighting training areas where AFFF was used repeatedly over decades created concentrated PFAS plumes in the underlying alluvial aquifer along the Missouri River. The Air Force is conducting a remedial investigation under CERCLA authority, with interim actions to provide clean water where needed.
Montana's agricultural sector – primarily cattle ranching and grain farming – creates more diffuse water quality impacts. Nitrate from fertilizer and livestock waste has been detected in shallow wells across the agricultural eastern part of the state, though generally at lower concentrations than in the Corn Belt states.
The state's headwaters position gives it an unusual responsibility and opportunity. Water that originates in Montana flows to the Pacific (via the Columbia), the Gulf of Mexico (via the Missouri-Mississippi), and Hudson Bay (via the Saskatchewan system). Protecting source water quality in Montana benefits downstream communities across the continent.
Missoula's aquifer – the Missoula Valley Aquifer – deserves special mention. This alluvial deposit, left by glacial Lake Missoula's catastrophic floods at the end of the last ice age, holds an enormous volume of cold, clean groundwater. The city's water supply draws from this aquifer with minimal treatment needed. Protecting the aquifer from surface contamination is a central priority of Missoula's land use planning.
Check your address to see available data for your location. Montana's water is among the best in the nation, but localized risks from military operations and mining legacy mean your specific location still matters.