Prior Appropriation Doctrine Law and Legal Definition

Prior appropriation doctrine is the rule that among the persons whose property borders on a waterway, the earliest users of the water have the right to take all they can use before anyone else has a right to it.

It is a doctrine that prevails in some American jurisdictions that the person who first diverts and applies to a beneficial use the waters of a stream of public right has a prior right of continued use to the extent of his appropriation. [Wyoming v. Colorado, 259 U.S. 419 (U.S. 1922)]