How is the allocation of surface water determined in Arizona?

The allocation of surface water in Arizona is determined by the principle of first in time, first in right. This doctrine, often referred to as the "prior appropriation" doctrine, operates on the basis that the first individual or entity to take water from a source for beneficial use has a legal right to continue using that amount of water, even in times of scarcity. This principle is fundamental to Arizona's water law, as it provides a predictable and orderly method for allocating limited water resources among users.

The first-in-time aspect ensures that those who established their rights to water first maintain their priority over those who may claim it later. This system incentivizes the efficient use of water, as users seek to maximize their benefit from the resources they have appropriated.

Alternative options, such as allocation by a governmental agency, democratic voting, or random lottery, do not reflect the established legal framework governing water rights in Arizona. While governmental agencies may oversee and manage water resources, they do not determine rights based on any means other than the prior appropriation doctrine.