Idaho Rainwater Harvesting Universal Diffused Surface Water Right

Idaho's prior appropriation water rights doctrine governs all surface and groundwater under Idaho Code Title 42, administered by the Idaho Department of Water Resources. The 2008 Idaho Attorney General opinion clarified that diffused surface waters, including rainwater on rooftops and surfaces before reaching natural watercourses, may be captured by the landowner without a water right or permit. No statewide volume cap exists for residential rainwater harvesting. However, water collected from natural channels, springs, or creeks remains subject to appropriation. No municipality may prohibit lawful rainwater harvesting that complies with state water law. Potable use requires compliance with state drinking water treatment standards.

Diverting water from natural channels without a water right violates Idaho Code 42-201. Water rights interference may trigger civil action by injured appropriators.