Water Law and the Colorado River Compact

In the arid West, water is more consequential than gold. Colorado learned this early and built a legal doctrine around it.

The principle of prior appropriation holds that the first person to divert water from a stream and put it to productive use holds the oldest and most secure water right. In times of shortage, junior rights are cut first. Senior rights are satisfied in full. Colorado developed this doctrine in the mining era of the eighteen fifties, when prospectors needed reliable water for sluicing and could not depend on owning land next to a stream. The doctrine has governed water use in the state ever since.

The Colorado River Compact of nineteen twenty-two extended this logic to an entire river basin. Negotiated by delegates of the seven states over many months and signed near Santa Fe, New Mexico, the compact divided the Colorado River between an upper basin, which includes Colorado, Utah, Wyoming, and New Mexico, and a lower basin, which includes California, Arizona, and Nevada. Each basin received an annual allocation of water. Colorado, as the state where the river begins, retained rights to a large share of the upper basin allocation.

The compact was built on flow estimates that have since proven too high. The negotiators assumed the river carried more water on average than it actually does in most years. A century of drought data, combined with population growth across seven states and Mexico, has stressed the system to a point that the compact's framers could not have foreseen.

The river that begins in Colorado supplies water to roughly forty million people. The arguments about how to share it are nowhere near settled.