prior appropriation doctrine

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The prior appropriation doctrine grants rights over surface water and groundwater in order of seniority, where the first person to divert water away from its natural source and apply it for some beneficial use acquires a priority right to continuously use the water. The scope of the right is limited to the reasonable amount of water required for the beneficial use to be served. Therefore, under this doctrine, a water right is not obtained from rights in the land but from appropriating the water for a beneficial use. See also: Sacramento Grazing Ass'n, Inc. v. United States.

The person granted the water right can use the specific amount of water required for the beneficial use without the threat of subsequent claims or accounting for the needs of other water users. The priority right acquired by the earliest user of the water is maintained even during times of drought and water shortage. See also: Westlands Water Dist. v. United States. However, the right is only maintained through the continued beneficial use of the water. See also: Colorado River Water Conservation Dist. v. United States

In the seminal 2011 Supreme Court case, Montana v. Wyoming, Justice Thomas, writing for the majority, noted that Wyoming’s irrigation improvements increased the amount of water it used from the Yellowstone River only up to the amount of water originally required for beneficial use. Thus, the improvements did not violate the prior appropriation doctrine, despite the detrimental impact of increased water usage on those downstream of the river. Thomas analogized to a “farmer who traditionally consumes only 50% of the water applied to his land [being] free to change his crop or method of applying water so as to increase his consumption to 60%” in finding Wyoming’s improvements lawful.

A vast number of Western states have embedded the prior appropriation doctrine not only in common law but also through explicit statutory directives. For example, under the New Mexico Constitution Article XVI, Section 2, all unused water is explicitly stated to be “public” and subject to appropriation for beneficial use. Statutory guidance from the State of Washington similarly states that public water can “only be acquired by appropriation for a beneficial use and . . . the first in time shall be the first in right.“ Contrast with riparian doctrine. See also riparian rights.

[Last updated in April of 2024 by the Wex Definitions Team]