In Arizona, under which doctrine is all non-Colorado River water mostly adjudicated?

In Arizona, the doctrine under which all non-Colorado River water is mostly adjudicated is the doctrine of prior appropriation. This legal principle is grounded in the concept of "first in time, first in right," meaning that the first person to divert and use water has the senior right to it.

This system promotes the efficient use of water resources by providing certainty in water rights. Under prior appropriation, water rights are allocated based on the priority date of the appropriation—those who established their water rights earlier have precedence over those who do so later. This has important implications for water management in the state, particularly in times of scarcity, as it determines who has the legal right to use available water resources.

The other doctrines listed pertain to different aspects of water law and rights. For example, the doctrine of equitable apportionment primarily addresses issues of water allocation between states or large geographic areas rather than individual rights. The doctrine of constructive possession generally relates to real property and does not specifically address water rights. Lastly, the doctrine of first usage is a less commonly referenced concept in water law compared to prior appropriation and does not dominate in Arizona's legal framework.