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.