Article 5

5.2 Application

In the case where the quantity or quality of water in an international watercourse is insufficient to satisfy the needs of all riparian states – i.e. a conflict of uses exists – the application of the principle of equitable and reasonable utilisation follows a two-step approach. First, one has to ask whether the relevant uses are reasonable; and second, the competing reasonable uses have to be reconciled on the basis of equity.

States A (developing country, upstream) and B (downstream) share an international watercourse. State A intends to increase the diversion of the flow of the river for its irrigation canals and informs state B of its plan. In its communication state A assures state B that the increase of the withdrawal will be negligible – only a very small percentage of the overall flow – but will bring huge benefits for state A’s food security. In its reply state B argues that instead of wasting even more water in its ancient irrigation canals, state A should rather invest in drip irrigation systems or just buy the required amounts of food from state B. While state B acknowledges that the planned increased withdrawal of water is only marginal, it fears that ‘giving in’ every time A wants to use more water to feed its rapidly growing population, could interfere with state B’s plans to extend its holiday resorts along the river.

While B is right in claiming that state A’s plans to grow crops in additional areas is not the most efficient or beneficial use of the watercourse, the question whether the use is reasonable follows a different line of argument. The requirement of ‘reasonableness’ does not demand for the most economical use (here, using the most advanced irrigation technology), but rather follows the contemporary conception of rationality which takes country specific factors into account – e.g. the stage of development. Considering that the planned utilisation of the shared waters will most likely also be ‘sustainable,’ since state A took into account the long-term carrying capacity of the watercourse, the use might be deemed to be reasonable.

After establishing that the utilisation of the international watercourse is reasonable, states A and B have to debate whether it is also equitable. Here, again, the argument of state B does not hold, since it is unlikely that using the shared water resource for its envisaged upgrade of the tourism activities along the river bank will be deemed of higher value than state A’s demand for irrigation. It would be advisable, however, for states A and B to design a long-term management plan for the whole basin where future needs of both states will be considered, and potentially win-win scenarios could be developed. Only then can further frictions between the riparians be avoided.

When looking at the operational aspects of the principle of equitable and reasonable utilisation – and especially while trying to reach an equitable (re)allocation of the water resource – one has to read Article 5 with both Article 6 and Article 10 in mind (the former providing for a non-exhaustive list of factors which has to be considered and weighed when deciding whether a use is equitable and reasonable; and the latter for determining that no use of a transboundary watercourse has inherent priority).

	Figure 2.2 The Application of Equitable and Reasonable Use (Source Authors)
	Video: Owen McIntyre The concept of equity in international water law
	Video: Alistair Rieu-Clarke What is the relationship between the Principle of Equitable & Reasonable Use and the No-Significant-Harm Rule in the UNWC?