International law provides a wealth of precedents on water use rights and obligations for both upper and lower riparians. The customary international law for transboundary fresh water resources provide for equitable utilisation, the Madrid Declaration of 1911 says that the regime of rivers and lakes, contiguous or successive, could not be altered by one state to the detriment of a co-riparian without the consent of the other. This law was also an off-shoot of the same customary law.

Similarly, the Article 2 of Declaration of Montevideo 1933 points that no state may, without the consent of the other riparian state, introduce into water courses of an international character, for industrial or agricultural exploitation of their waters, any alterations which may prove injurious to other interested states.

Article 4, Chapter 2 of Helsinki Rules 1966 on the Uses of the Waters of International Rivers’, adopted by the International Law Association, insists that, “Each basin State is entitled, within its territory, to a reasonable and equitable share in the beneficial uses of the waters of an international drainage basin”.

UN Convention on the Law of the Non-navigational Uses of International Watercourses adopted by General Assembly on May 21, 1997, is the treaty governing shared freshwater resources and is universally applicable to all member states.

UN Convention contains 37 articles arranged in seven parts. Yet Article 5, contained in Part II, reflects the principle that is widely regarded as the cornerstone of the Convention, and indeed the law in the field for equitable and reasonable utilisation and participation. It requires that a State sharing an international watercourse with other States utilise the watercourse, in its territory, in a manner that is equitable and reasonable vis-à-vis the other States sharing it.

With the UN Convention having been ratified by 36 states – after 17 years of adoption by the UN General Assembly – it has entered into force on August 17, 2014. While the majority of the countries have opted to remain outside its scope for now, the convention, however, establishes an important international law governing cross border watercourses declaring water rights of all riparians as sacrosanct and non-violable.

The customary international law, declarations, Helsinki rules and UN convention on the subject establishes two important principles for all river basins: one, that the first right over the water of the rivers is that of the people living in the basin, and the second that the shared waters could neither be stopped nor diverted without the consent of the other riparian state.

For the Indus rivers water, therefore, established international law prohibits India as an upper riparian to stop or divert waters of the rivers to the detriment of the people of Pakistan without the prior and explicit approval from Pakistan beforehand.