Riparian rights is a water law doctrine granting landowners adjacent to a natural water body the right to make reasonable use of that water. It is the predominant system in the eastern United States and much of the world.
The riparian rights doctrine grants owners of land bordering natural water bodies (rivers, streams, lakes) the right to make reasonable use of the water for purposes such as domestic supply, irrigation, livestock watering, and recreation, provided that such use does not unreasonably diminish the quantity or quality of water available to other riparian landowners. Unlike prior appropriation, riparian rights are not based on priority of use but rather on land ownership; all riparian owners share co-equal rights to the water, and during shortages, all users must reduce their use proportionally. The doctrine originated in English common law and was adopted in the eastern United States, where abundant rainfall historically made water allocation conflicts less contentious than in the arid West. The reasonable use standard is inherently flexible but also uncertain, as what constitutes reasonable use depends on factors including the nature and purpose of the use, the size of the watercourse, and the impact on other users. Many eastern states have supplemented or partially replaced the riparian doctrine with regulated permit systems to provide more certainty and control over water allocation. Riparian rights are generally considered appurtenant to the land and cannot be separated from riparian property, though this varies by jurisdiction. Climate change, population growth, and competing demands are increasing water conflicts in traditionally water-rich eastern states, prompting reforms that incorporate elements of both riparian and appropriative systems.