Priority of Uses in International Water Law

The raison d’être of international water law is that it provides States with a toolkit to equip them to deal with complex problems relating to the joint use and sustainable management of transboundary freshwater resources. The principle of equitable and reasonable utilization is one such tool in this toolkit. When applying the equitable and reasonable utilization principle to a specific transboundary watercourse, States sharing that watercourse must decide which water uses are more important than others. But the general rule is that no water use takes a priori priority over others (this is the so-called no-inherent-priority rule). This paper examines three ways in which this no-inherent-priority rule can be relativized, by recognizing a certain degree of priority to certain categories of water uses. Based on an assessment of previous State practice, it is suggested that (1) existing uses enjoy a certain degree of priority over new uses; that water uses that are (2) more beneficial to a greater number of people and are less damaging to other uses and the freshwater ecosystems, enjoy priority; and that water uses that (3) immediately satisfy vital human water needs enjoy priority. States need some general guidance in identifying which water uses normally take priority in defined circumstances, and this paper provides such guidance, thereby making the tool more effective. States can decide to derogate from these general rules if the circumstances so require; they are, of course, not legally binding on them.