This work examines the international legal theory and State practice related to the non-navigational uses of international watercourses. To determine the international rules that apply in this field, the codification work of the UN International Law Commission, the International Law Association and the "Institut de droit international" is critically analysed and compared with representative State practice. The 1997 UN Watercourses Convention, and its evolution, is given special attention

It is concluded that the principle of reasonable and equitable utilisation is the primary rule of international law that governs watercourse States. The non-significant harm rule is one factor to be considered in what qualifies as an "equitable and reasonable" use. Rules of procedure, such as exchange of information, prior notification and peaceful settlement of disputes, facilitate implementation of the substantive rule of equitable and reasonable use. The 1997 Watercourse Convention embodies this approach and should be considered in this context