Key Points

• The Convention adopts a wide definition of the ‘uses’ of international watercourses, designed to capture multiple economic, social and environmental uses of water (Article (1)).
• The Convention applies to navigational uses but only to the extent that other water users may affect navigation or vice-versa, e.g. pollution from vessels.
• The Convention applies to international  ‘watercourses and their waters’, and emphasises that both the water channel itself, and interrelated components, as well as the waters contained therein are subject to its provisions’ (Article 2(a)). ‘Watercourse’ is specifically defined as ‘a system of surface waters and groundwaters constituting by virtue of their physical relationship a unitary whole and normally flowing into a common terminus’ (Article 2(a)).
• The Convention appliers to an ‘international watercourse’ defined as ‘a watercourse, parts of which are situated in different states’ which covers ‘watercourse systems’ that cross international boundaries (Article 2(a) and (b)).
• The Convention applies to groundwater systems  but only to the extent that an aquifer85 is connected hydrologically to a system of surface waters, parts of which are situated in different states, which therefore excludes confined aquifers86 (Article 2(a) and (b)).
• The definition of a ‘watercourse state’ (Article 2(c)), implies that the rights and duties established by the Convention apply exclusively among contracting parties and only to ‘other states’ (riparian non-contracting states) when they are vulnerable to transboundary harm through an international watercourse. Although, the rules of customary law as codified by the Convention still apply to non-contracting states (see Section 4.1).
• In terms of existing and new agreements, Article 3 and Article 4 require watercourse states to consult with each other on the adjustment and application of the provisions of the Convention, and where necessary harmonise the Convention’s principles with the specific watercourse agreements.
• Art 3(3) and Art 4(2) of the Convention provide that all watercourse states may become a party to any agreement that only refers to a portion of the basin or to a specific project or use if they may be affected by such an agreement. If riparian parties choose not to become a party to such an agreement, the agreement still cannot adversely affect, to a significant extent, the use of the resource by non-participating riparians without their express consent (Article 3(4)).

85 The word ‘aquifer’ refers to a ‘permeable water-bearing geological formation underlain by a less permeable layer and the water contained in the saturated zone of the formation’. International Law Commission, Draft Articles on the Law of
Transboundary Aquifers (21 February 2008) UN Doc. A/CN.4/591 Art. 2.

86 See Section 2.1 for commentary on the nuances and meanings of these terms as they have developed through the work of the ILC on groundwater.

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Groundwater Systems