Water law in the western United States generally follows the appropriation doctrine which developed due to the scarcity of water in that area.

Most western states, naturally drier, generally follow the prior appropriation doctrine, which gives a water right to whoever first puts water to beneficial use.

Colorado, where the prior appropriation doctrine first developed, was generally looked to as the model by other Western states that adopted the prior appropriation doctrine.

Each state exhibits variations upon the basic principles of the prior appropriation doctrine.

Consequently, the rights of a riparian owner under the prior appropriation doctrine are always subject to the rights of other riparian owners who can demonstrate a more economically efficient use.

Under the prior appropriation doctrine, water rights are "first in time, first in right".

The use of water in Colorado and other western states is governed by what is known as the prior appropriation doctrine.

The prior appropriation doctrine is based on the concept of "First in Time, First in Right."

Arizona follows the prior appropriation doctrine for determining water rights.

Specifically, the federal suit was about rights the federal government had previously reserved, rather than rights based on the prior appropriation doctrine.