In Montana, the ownership of water, including rainwater, is governed by state law which holds that all waters within the state are owned by the state on behalf of its citizens. Individuals do not own the water but can hold legal rights to use it through recorded water rights or permits under the state’s prior appropriation doctrine (“first in time, first in right”). This means water use rights are granted and regulated by the state, not based on ownership of the water itself.
Specifically for rainwater, Montana places no restrictions on rainwater harvesting. Homeowners and landowners are legally allowed to collect and use rainwater without requiring a water right or permit. This practice is legal and encouraged, as long as it does not interfere with existing water rights. Rainwater harvesting is typically limited to collection from rooftops and used for non-potable or domestic purposes, but the state does not regulate or prohibit it. Collecting water from streams or other surface waters without permits remains regulated and illegal if not authorized.​
Thus, while the state owns all waters, private citizens in Montana may legally harvest rainwater from their property without owning the water itself. Water rights primarily govern the use of surface and groundwater resources, but rainwater catchment is an exception enabling conservation and beneficial use without complex permitting.
This framework reflects Montana’s balance between state water resource management and individual water use freedoms, including promoting sustainable rainwater collection practices. For detailed guidance, Montana’s Department of Natural Resources and Conservation (DNRC) offers resources on water rights and rainwater harvesting.
SOURCES
[1](https://dnrc.mt.gov/Water-Resources/Water-Rights/)
[2](https://dnrc.mt.gov/Water-Resources/Water-Rights/Understanding-Water-Rights/)
[3](https://www.ntotank.com/blog/rainwater-harvesting-laws-regulations-and-rights-by-us-state)
[4](https://worldwaterreserve.com/is-it-illegal-to-collect-rainwater/)
[5](https://4perfectwater.com/blog/rainwater-harvesting-laws)
