Many states allocate water rights based on which principle?

The doctrine of prior appropriation is a principle that many states use to allocate water rights, particularly in the western United States. This system operates on the concept of "first in time, first in right," meaning that water rights are granted to individuals or entities that first divert and use water from a particular source. Under this doctrine, once water has been appropriated for beneficial use, rights to that water can be established and may be secured even if the original user is not the landowner next to the water source.

This approach encourages users to develop and utilize water resources in ways that promote efficiency and economic development. The doctrine of prior appropriation is crucial in arid regions where water is scarce and demands are significant. In contrast, the riparian theory and littoral theory pertain more to water rights associated with landownership adjacent to rivers or lakes and are commonly applied in areas where water is more abundant. Accretion refers to the gradual increase of land or property due to natural forces and does not specifically relate to water rights allocation.