In Washington state, rainwater is considered a public resource owned collectively by the people, not by individual landowners, and is managed under the prior appropriation doctrine by the Department of Ecology. This system emphasizes “first in time, first in right,” where water rights are granted for specific beneficial uses, amounts, places, and periods, even for precipitation captured on private property. Landowners must secure a water right permit for most diversions, including rainwater harvesting beyond minor exempt uses like small domestic rooftop collection.​
Water Rights Basics
Water rights require state approval since the 1917 Water Code, prioritizing senior users during shortages and protecting instream flows for fish and ecosystems. Exemptions exist for limited domestic groundwater withdrawal (e.g., up to 5,000 gallons daily in some areas), but larger rainwater systems for irrigation or commercial use need permits to avoid impairment of existing rights. Adjudications in Water Resource Inventory Areas (WRIAs) resolve claims through court, issuing certificates as the strongest legal proof.​
Rainwater Harvesting Rules
Rainwater from roofs or surfaces falls under surface water rules if diverted, requiring a permit unless exempt; Ecology encourages conservation but enforces against unpermitted use. Trust Water Rights Program holds rights for instream flows, preventing private hoarding, while changes to rights (e.g., relocating use) need certified approval. Many basins are closed to new appropriations due to over-allocation, pushing conservation like drip irrigation.​
Conservation Mandates
Users must prove beneficial use (e.g., irrigation, municipal) without waste, with metering and reporting often required; relinquishment occurs after five years of nonuse. Instream flow rules block junior rights if they harm established minimums, balancing human needs with environmental protection amid climate pressures. Land transactions should verify attached water rights via Ecology records to maintain value.
SOURCES
[1](https://www.whatcomcounty.us/DocumentCenter/View/87332/WRIA-1-Washington-Water-Right-Glossary)
[2](https://www.reddit.com/r/Washington/comments/1hxxc6t/water_rights_in_washington_state/)
[3](https://www.re-sources.org/2019/09/water-rights-101-how-do-we-allocate-water-in-washington/)
[4](https://www.montgomerypurdue.com/blog/washington-water-law-the-basics/)
[5](http://irrigation.wsu.edu/Content/Fact-Sheets/FSWR001-WA-Water-Rights-v3.pdf)
