First in Time, First in Right: Prior Appropriation and Tribal Water – Alice Le Bihan

Do you know the name of the colonial-era framework that still governs how water is used across much of the West?

A Phoenix suburb, a California farm, a Navajo family: every drop of Colorado River water these users are legally entitled to exists within a ranking system. This system, known as prior appropriation, dictates who gets water first when the river runs short.

What prior appropriation is. Prior appropriation runs on the notion of “first in time, first in right.” Whoever first diverted water and put it to beneficial use (irrigation, mining, municipal, industrial use) holds a priority date. In a shortage, the water is filled in strict order of seniority. The most senior right holder is entitled to 100% of their allocation before the next-most-senior can fill theirs, meaning junior users can be cut off entirely while senior ones go unaffected.

Where it came from. The doctrine of prior appropriation finds its legacy in the extractive economy. During the California Gold Rush, miners diverted water miles from its natural channel to work claims. Courts and mining camps prioritized settlers who staked and used the water first, and Colorado’s Supreme Court formalized this use-based property system in 1882, which became the template for most western states. In short, the doctrine was built by and for settlers moving water toward mines, farms, and growing towns, not for the Indigenous communities already living along the river.

Why it binds users together. No single user’s water security exists in isolation because prior appropriation ranks every right holder on the same river. A farmer’s allocation depends on how many people hold older, senior claims above them. A city’s water planning depends on knowing where it sits in that queue during a drought. This is exactly why the current post-2026 negotiations for the Colorado River matter so much: the basin is essentially one long priority list, and any uncertainty about where a major claim sits creates uncertainty for everyone standing behind it in line.

What this means for tribes. Tribal water rights, which are often tied to the creation of reservations, regularly carry priority dates older than other users. Under prior appropriation’s own rules, this makes tribal nations some of the most senior water right holders on the river. In practice, that seniority has been limited both by how tribal water gets quantified in state courts and federal settlements, and by the absence of federally funded infrastructure to divert and deliver it. This system often leaves tribal rights as “paper water,” a number on a priority list, not water in a pipe.

In a time of uncertainty, it is worth recognizing the paradox of prior appropriation. This doctrine was created to facilitate settlement and resource extraction in the West, and it is now one of the primary tools Tribes use to reclaim water rights that it was never designed to protect. Therefore, the same system that promised certainty through fixed allocations has now become a source of uncertainty as unresolved Tribal claims, declining flows, and competing demands reshape the future of the Colorado River.