Part II

General Principles

The principle of ‘Equitable and Reasonable Utilisation’ is the cornerstone of international law related to transboundary watercourses.
It entitles a watercourse state to an equitable and reasonable share of the uses or benefits of the particular watercourse and creates the correlative obligation not to deprive other states of their respective rights.
It is based on the allocation theory of ‘limited territorial sovereignty’ which stipulates that watercourse states enjoy equal rights to the utilisation of an international watercourse.
Article 6 provides an indicative list of factors and circumstances to be taken into account when determining what constitutes an equitable and reasonable use.
The Legal Assessment Model developed by the IHP-HELP Centre for Water Law, Policy and Science provides a useful tool for identifying, measuring and evaluating the relevant factors and circumstances applicable to equitable and reasonable use.
States are obliged to take all appropriate measures not to cause significant harm to other watercourse states, however, some significant harm may be tolerated – in very limited circumstances – where it can be established to be equitable and reasonable.
While no use of a transboundary watercourse has inherent priority over others, special regard has to be given to vital human needs and the protection of the ecosystems of international watercourses.