International Water Law: Reasonable Utilization

Margaret J. Vick

Abstract

Reasonable utilization of shared waters is a centuries old principle of riparian law. It is one half of the foundational principle of international water law that requires the equitable and reasonable utilization of international waters. The principle of equitable utilization is extensively developed through treaties, conventions, case law and the writings of scholars of the law of non-navigational uses of international watercourses. However, the principle of reasonable utilization has received little attention. This article examines the relationship and commonalities between riparian reasonable use and the principle of international law and traces the inclusion of the requirement of reasonable utilization in international instruments. It concludes with a case study of a small stream in the western United States, the Vermejo River using the decisions from the United States Supreme Court analyzing the relationship between equitable apportionment of a transboundary river and reasonable utilization.