Cascade County, Montana: drinking water report. Cascade County in central Montana has about 82,000 residents, with Great Falls as the county seat.
Cascade County in central Montana has about 82,000 residents, with Great Falls as the county seat. The Missouri River provides the primary water source, with the City of Great Falls operating the treatment and distribution system. Malmstrom Air Force Base – an active intercontinental ballistic missile base – sits on the eastern edge of the city.
Malmstrom AFB has confirmed PFAS contamination from AFFF firefighting foam. According to the Air Force's 2024 environmental investigation, monitoring wells near the base fire training area show PFOS at 52 ppt – well above the federal MCL. The contamination plume extends off-base into residential areas east of the city.
The Missouri River at Great Falls benefits from a relatively undeveloped watershed upstream. According to Montana DEQ's 2024 water quality report, the river at the intake shows low contaminant levels, with TDS averaging 280 mg/L. The Giant Springs – one of the largest freshwater springs in the country – contribute clean water to the river just upstream of the city.
Great Falls benefits from clean Missouri River water, but residents near Malmstrom AFB face documented PFAS exposure. The Air Force has been conducting residential well testing in the affected area – contact the base environmental office if you are on a private well nearby.
Check your water for data at your address. For PFAS near the base, reverse osmosis provides the strongest household protection. For the clean river supply, a carbon filter addresses taste and chlorine. Our water filter guide covers both scenarios. Get your detailed report for local data, and visit our Montana page for statewide patterns.
Drinking water is one exposure route. These federal datasets also cover Cascade County, MT.
The EPA places Cascade County, MT in Zone 1 - the EPA's highest-risk category, where the predicted average indoor radon level is above 4 pCi/L. Zone maps predict an area's radon potential from geology and existing indoor readings; they say nothing about a specific house. Testing is the only way to know your own level.
67% of homes in Cascade County, MT were built before 1980, and 21% before 1950. Residential lead paint was banned in 1978, so housing age is the strongest available proxy for lead-paint exposure. This describes the county's housing stock, not any one home.
Modelled annual fine-particle pollution (PM2.5) in Cascade County, MT averages 5.5 µg/m³, within the EPA's annual standard of 9 µg/m³. These are CDC modelled county estimates rather than readings from a specific monitor.
How radon zones work · Air quality by county · Lead exposure guide