Legal Definitions - Prior appropriation doctrine

The Prior Appropriation Doctrine is a legal principle primarily used in drier regions, particularly in the western United States, to allocate rights to use surface water and sometimes groundwater. It establishes that the right to use water is granted to the first party who diverts it from its natural source and applies it to a beneficial use. This means that an individual or entity who began using water earlier for a recognized purpose, such as irrigation, mining, or municipal supply, holds a superior right to that water compared to those who started using it later, even if the later users are physically closer to the water source. The core idea is "first in time, first in right."

Here are some examples illustrating the Prior Appropriation Doctrine:

• Agricultural Use: Imagine a river flowing through a desert valley. In 1880, a farmer, Mr. Jones, builds a ditch to divert water from the river to irrigate his alfalfa fields. In 1920, a new farmer, Ms. Smith, settles upstream and also begins diverting water from the same river for her fruit orchard. Under the Prior Appropriation Doctrine, Mr. Jones has a "senior" water right because he began his beneficial use of the water earlier. If there's a drought and the river's flow is insufficient for both, Mr. Jones's water needs must be fully met before Ms. Smith can take any water, even though her farm is upstream.

• Industrial and Municipal Development: Consider a mining town established in 1895 that built a pipeline to bring water from a mountain stream for its ore processing and residents. Years later, in 1940, a new resort community develops further downstream on the same stream and also seeks to use its water for hotels and golf courses. The mining town's water right is senior because its beneficial use (mining and municipal supply) began earlier. In times of low stream flow, the resort community's water use would be curtailed to ensure the mining town's established needs are met first.

• Competing Public Uses: A city was founded in 1905 and constructed a reservoir and pipeline system to supply drinking water to its growing population from a nearby river. Decades later, in 1960, a state agency decides to build a large recreational lake on the same river, intending to divert a significant portion of the river's flow to maintain the lake's water level for boating and fishing. Because the city's beneficial use (public water supply) began earlier, its water rights are senior. If the river's flow drops, the city's water supply for its residents takes precedence over maintaining the recreational lake's water level, and the lake's diversions would be reduced first.