Which doctrine governs water rights in Arizona?

In Arizona, the doctrine that governs water rights is the doctrine of prior appropriation. This doctrine is based on the principle of "first in time, first in right," which means that the right to use water is granted to those who first put the water to beneficial use. This system is particularly important in arid regions like Arizona where water is scarce, allowing for structured allocation of water resources.

Under the prior appropriation doctrine, water users must demonstrate that they are actively using water for a beneficial purpose, such as agriculture or municipal supply. This approach contrasts with the riparian rights doctrine, which ties water rights to land ownership adjacent to water sources. Since most of Arizona's water resources are not naturally flowing and are often distant from immediately adjacent landowners, prior appropriation is better suited to manage these resources effectively.

Additionally, the notion of reasonableness primarily relates to how water use impacts others and is not the primary framework governing rights in Arizona. The public trust doctrine encompasses governmental responsibility for protecting and managing natural resources but does not dictate individual water rights in the same way that prior appropriation does. Thus, prior appropriation remains the cornerstone of water rights management in Arizona.