Yes. Rainwater collection is fully legal in Montana, with no state limits on how much you can collect from your roof.
What Montana law says
Montana places no state-level restrictions on residential rainwater harvesting. You can install as many barrels or cisterns as your property supports, and no permit or registration is required. No state restrictions. As always, check for HOA covenants or local ordinances before installing a larger system.
How much water a Montana roof can collect
Montana averages about 15 inches of rain per year. On a typical 1,200 square foot roof at 85% collection efficiency, that works out to roughly 9,500 gallons a year currently running into your storm drain. A single one-inch storm delivers about 635 gallons, enough to fill 13 standard 50-gallon barrels.
Average annual rainfall in Montana.
Gallons per year from a typical 1,200 sq ft roof.
Approximate annual value at municipal water rates.
Your roof and rainfall will differ; run your exact numbers in the rainwater calculator.
The right setup for Montana’s climate
With about 15 inches of rain a year, Montana is a dry-climate state where storage capacity matters most. Storms are rare, so when one comes you want to catch as much as possible: a 65-gallon barrel, or two linked 50s, beats a single small barrel that overflows in the first hour.
Rain Wizard 65 Gallon, reviewed against our independent testing criteria. See all six models side by side.
Common questions
Is it illegal to collect rainwater in Montana?
Do I need a permit for a rain barrel in Montana?
Does Montana offer incentives for rainwater harvesting?
Sources
- Rainplan, 50-State Rainwater Collection Guide (2026)
- State statutes and water agency guidance for Montana
- NOAA National Centers for Environmental Information, annual precipitation normals
- US EPA WaterSense, Outdoor Water Use fact sheet
Educational content, not legal advice. Laws change; confirm current rules with your state water agency.