Despite the fact that numerous international watercourses are regulated by treaties, many of these agreements are now outdated, incomplete, or have not been adhered to. This situation, coupled with the increasing demand for freshwater supply, magnify the possibility of water conflicts, despite the existence of a large body of conventional law in the field. Will the rules elaborated by the UN succeed in providing acceptable direction for the international community in their concerns over water? Water Law and Transboundary Watercourses examines the evolution of the principles of equitable utilization and no harm as rules of customary international law that have come to define legitimate State activity regarding international water use. The key issues addressed are: (1) What is the normative content of the principles of equitable utilization and no harm as they relate to international watercourse law? (2) What is the hierarchical relationship between the two principles? While the answer to the first question is important because it defines the rules applicable in the area, the response to the second question is critical as it determines the rule that governs international water-use where the demand exceeds the supply, a conflict-of-uses situation. The majority of water problems in the future will fall into this category underlining the need to resolve these critical issues.