Montana Statewide Rule

Montana Rainwater Collection Allowed Under Water Use Act

Few RestrictionsApplies statewide across Montana (2026)

Montana law permits rainwater harvesting from rooftops for non-consumptive uses without a water right. Cisterns and storage are not separately regulated by the state, but collection cannot interfere with senior downstream water rights.

Key Facts

Rooftop collection: Generally allowed
Statute: MCA Title 85, Ch. 2
Large impoundments: May require permit
Doctrine: Prior appropriation

Source: Montana Legislature

Full Breakdown

Montana follows the prior appropriation doctrine under Title 85, Chapter 2 MCA. Rooftop rainwater collection for landscape irrigation and non-potable household use is generally treated as de minimis and does not require a DNRC permit. However, large-scale impoundments, ponds, or pit reservoirs that capture runoff may need a water right under MCA 85-2-306. The state has not preempted local building or plumbing rules around cistern installation, but the underlying right to capture rooftop water is governed by state water law rather than by city ordinance.

Violations & Penalties

Diverting runoff via large impoundments without a water right can trigger DNRC enforcement, civil fines, and orders to remove unauthorized structures under MCA 85-2-122.

Frequently Asked Questions

Is rooftop rainwater harvesting legal in Montana?

Yes. Collecting rainwater from your roof for landscape or non-potable household use is allowed without a state water right and is not preempted against by Montana law.

Do I need a permit for a backyard rain pond?

Excavated ponds or pit reservoirs that capture more than de minimis runoff may require a DNRC water right under MCA 85-2-306. Check with your regional DNRC office.

Sources

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