Arizona v. California and the Equitable Apportionment of Interstate Waterways

Fifty years ago, the Supreme Court sided with Arizona in its decades-long dispute with California over the waters of the Colorado River. At the heart of the case’s legacy is a paradox: There is widespread agreement that the Court reached the right result as a matter of policy, giving Arizona the water it needed to develop a dynamic, modern economy. Yet there is equally widespread agreement that the Court’s reasoning was wholly unpersuasive, resting on a blatant misreading of a thirty-five-year-old federal statute. How can this be? Was there no legally principled way to rule for Arizona, where the equities in the case seemed to lie?

The answer is that the Court’s predicament was one of its own creation. In a series of rulings over the preceding half century, it had placed prior appropriation—the time-honored Western water law principle of first in time, first in right—at the center of its doctrine of interstate equitable apportionment of water. This doctrinal development threatened to make equitable apportionment distinctly inequitable in the Colorado River case.

This Article traces the Court’s equitable apportionment jurisprudence over the first half of the twentieth century. Through original archival research, this Article seeks to demonstrate that a majority of the Court felt constrained by the rule of interstate prior appropriation, leading it to resort instead to the dubious piece of statutory interpretation that has been so heavily criticized. Because equitable apportionment and prior appropriation are fundamentally at odds, the Court should abandon its overreliance on prior appropriation and treat existing use of water as merely one consideration to be weighed as part of a larger, multifactor balancing approach to equitable apportionment cases. Though a majority of the Court is generally reluctant to employ this sort of open-ended, subjective test (and with good reason), the unique nature of original jurisdiction equitable apportionment actions makes this approach the only appropriate one for dividing interstate waterways.