Though there are globally 263 transboundary river basins, many of them lack an agreement among the riparian states about how to share or to jointly manage the water resources. On a global level, there is no binding international agreement on transboundary water in force. Nevertheless, over the last century, a strong customary law has evolved. In 1911, the Institute of International Law published the Madrid Declaration on the International Regulation regarding the Use of International Watercourses for Purposes other than Navigation. It recommended to abstain from unilateral alterations of river flow and to create joint water commissions. In 1966, the International Law Association developed the Helsinki Rules on the Uses of the Waters of International Rivers. Their core principles are related to the «equitable utilization» of shared watercourses and the commitment not to cause «substantial injury» to co-riparian states. These principles are also the core of the UN Convention on the Law of the Non-Navigational Uses of International Watercourses, which was adopted by the General Assembly in 1997, after more than 25 years of preparation. Besides the confirmation of the principles of «equitable and reasonable utilization» and the «obligation not to cause significant harm», the convention contains regulations for the exchange of data and information, the protection and preservation of shared water bodies, the creation of joint management mechanisms and the settlement of disputes. However, it is still not in force as the necessary quorum of 35 countries' ratification has not yet been reached.

One reason for the reluctance of states to sign the convention is a certain vagueness of the core principles, which can lead to contradictions. An upstream country might claim its right to a previously unused «equitable share» of the water resources, which could cause economic harm to a downstream country that has used these resources for a long time. Whose rights and which principle have priority? And what exactly is an equitable share? Where is the borderline between a harm that has to be accepted and a significant harm? These questions are not answered in detail by the conventions, which only provide for the general principles and criteria. And this is very wise, because many of these questions can only be answered specifically for each basin, rather than applying to all. In this respect, the conventions provide a framework of joint principles on which regional agreements can be negotiated, not a blueprint for all river basins.

But there is a binding regional convention for the European and Central Asian region that made these two principles obligatory for its parties and provided a framework and guidelines for their application in specific river basins: the UNECE 1992 Convention on the Protection and Use of Transboundary Watercourses and International Lakes (the so-called Helsinki Convention). The Convention obliges parties to prevent, control and reduce transboundary impact, use transboundary waters in a reasonable and equitable way and ensure their ­sustainable management. Parties bordering the same transboundary waters shall cooperate by entering into specific agreements and establishing joint bodies. The Convention includes provisions on monitoring, research and development, consultations, warning and alarm systems, mutual assistance and exchange of information, as well as public access to information.

In Central Asia, Kazakhstan and Uzbekistan have signed it and the other states, though not formal members, are participating in some of its activities. Though the convention is now only applicable to countries of the UNECE region, thus not Afghanistan, Iran or China, an amendment intends to open it to others. As soon as this amendment is in force, the Helsinki Convention could also be a basis for water cooperation between Central Asia and its neighbouring states.