Governance & Policy
Prior Appropriation
Definition
Prior appropriation is a legal doctrine for allocating water rights in which the first person to divert water for a "beneficial use" acquires a right senior to all later claimants — "first in time, first in right". Rights are quantified, tied to continued beneficial use ("use it or lose it"), and in times of scarcity are satisfied in order of seniority, regardless of where along the watercourse the user sits.
References
Supports definition and framing.
Supports definition and framing.
Overview
How it is used
The doctrine governs surface water allocation across most western US states and influences water law reforms elsewhere; contrasts with riparian rights (eastern US, England) and permit-based systems.
Why it matters
Water allocation law decides who gets water as supplies shrink; understanding prior appropriation is essential to water security, environmental flow policy and water markets.