Water in Montana.
Montana's mining legacy drives arsenic and heavy-metal exposure in several watersheds. Butte and Anaconda communities have decades-long Superfund water-quality history.
How Montana regulates drinking water.
Federal SDWA primacy. No state MCLs stricter than federal. Active EPA Superfund oversight in Clark Fork watershed.
Montana Department of Environmental Quality — Public Water Supply
Montana's water history, in order.
The contamination events, regulatory shifts, and major settlements that define how this state thinks about drinking water today.
- 1983
Clark Fork Superfund site designated — among the largest in the U.S.
- 2019
Butte / Anaconda remediation milestones reached; long-term groundwater monitoring continues.
The actual water you drink.
The physical rivers, aquifers, lakes, and reservoirs that feed Montana's public water systems. Source quality is the foundation of tap quality — and where the long-term protection fights happen.
- riverClark Fork + Bitterroot Rivers
Missoula, Western MT.
- riverMissouri River
Central MT including Helena, Great Falls.
- riverYellowstone River
Eastern MT.
- aquiferMadison Aquifer
Major groundwater supply across central MT.
Source-water mix
~60% groundwater, ~40% surface water
Major cities served
Billings · Missoula · Great Falls · Bozeman · Butte
Who actually serves the water.
The largest public water systems in Montana by population served. Click your ZIP after to see the full live EWG report for your specific utility.
- Billings Public WorksBillings120Kserved
- Mountain Water CompanyMissoula80Kserved
- Bozeman Water DepartmentBozeman55Kserved
Where the contamination comes from.
Every state has a different industrial fingerprint. The industries below are the dominant historical and active contamination sources in Montana's drinking water systems.
Berkeley Pit (Butte) and Anaconda smelter legacy drove the country's largest Superfund site (Clark Fork). Coal extraction in the Powder River Basin adds groundwater concerns. Limited PFAS contamination relative to lower 48.
What state data flags most consistently.
Drawn from EPA SDWIS sampling records, EWG state summaries, and regional regulatory action over the past five years. Read the full deep dive on each.
Arsenic
A naturally occurring carcinogen. Highest in private wells and the rural Southwest.
Lead
A neurotoxic metal that leaches from old pipes and solder. No safe level for children.
Nitrate
Fertilizer and animal waste runoff. Acutely dangerous for infants under 6 months.
Risk isn't evenly distributed.
Residents in the Butte / Anaconda / Helena copper-corridor face the most-documented heavy-metal exposure. Rural well users face arsenic.
~30% on private wells — one of the highest in the U.S.
What's coming for Montana's water.
Snowpack decline reshapes Clark Fork and Missouri River summer flows. Wildfire burn-scar runoff into Bitterroot and Blackfoot watersheds. Glacier loss in Glacier National Park affects downstream hydrology.
Voluntary statewide
Montana DEQ provides voluntary technical assistance.
Five questions for your next Consumer Confidence Report.
Your utility is required to send you a Consumer Confidence Report annually. Most are dense and procedural. These are the questions worth following up on for Montana specifically.
- 1
If I'm in Butte / Anaconda corridor, is my system part of ongoing Superfund remediation?
- 2
Has my private well been tested for arsenic and heavy metals?
- 3
What is my system's pre-treatment turbidity range during spring runoff?
Most state regulators allow public records requests for the underlying lab reports behind your CCR — your utility should be able to provide them on request.
NSF/ANSI 58 reverse osmosis is the most universal solution for Montana's combined arsenic + heavy-metal profile.
We don't recommend brands — the NSF/ANSI certification number matters more than the name on the box.
This is the state. Your address is the answer.
State-level patterns don't tell you about your specific tap. Run your ZIP for the live EWG contaminant report on your utility — or build a personalized Water File for your household.
Source-water mix, utility counts, lead-service-line estimates, and private-well shares are approximate, drawn from EPA SDWIS public data and state primacy-agency summaries. Contaminant rankings reflect EWG state-level monitoring data and regional regulatory action — they are not exhaustive. Timeline events are publicly documented. See methodology for the full sourcing. Search EPA SDWIS for Montana