International water law (IWL) principles are often called upon to address disagreements and conflict between riparian states to a shared watercourse, with various parties invoking them to guide states’ behavior towards cooperative solutions that benefit the water resources as well as broader regional cooperation and peace. This essay argues that it is particularly important to acknowledge the role IWL principles play in negotiation processes, that is, in an ex ante and non-judicial function, providing a framework for cooperation and contributing to lawmaking, which makes them important tools of international relations and water diplomacy. First, IWL principles are particularly relevant in negotiation processes. IWL principles are thus not only relevant to legal adjudication or enforcement, but are also tools of international relations and diplomacy. Additionally, in their ex ante role, in the context of negotiations or other non-judicial interactions between riparian states, IWL principles can pose an inherent dilemma, as they can both provide a framework for negotiations and be the focus of negotiations, each dimension having implications for the effectiveness of negotiations and the likelihood of negotiated compromise outcomes. Third, in spite of this inherent dilemma and its possible negative repercussions on negotiation outcomes, the use of IWL principles in negotiations has a lawmaking function, contributing to the further development and strengthening of the overall legal regime for governing shared watercourses.

Could Turkey dam the Tigris and Euphrates and deprive its downstream neighbors of vital water resources? Could Brazil over-pump the Guarani Aquifer System to the detriment of the other aquifer states? Could Egypt put pressure on upstream Nile states and prevent them from developing river related infrastructure that might limit downstream flow? International law in the field of transboundary water cooperation has evolved and would appear to condemn unilateral practices such as the ones suggested above. However, hydro politics and the lack of reception of international water law instruments by many countries sometimes make it difficult to see international law properly reflected in the management of major rivers, lakes and aquifers around the world. In this essay, I first highlight what international law dictates when it comes to the tension between national sovereignty and transboundary water cooperation. I then explore how this tension plays out in the three examples noted above. Due to limited acceptance of the existing international, bilateral, or regional legal instruments, the resolution of the tension between national sovereignty and transboundary water cooperation will often be left to customary international law.

The relationship between the principle of equitable and reasonable utilization and the obligation against causing significant harm has been the most challenging issue in the long history of the evolution of international water law. The purpose of this essay is to discuss the genesis of the debate on the relationship between the two concepts, present the opposing positions of the different riparians thereon, and clarify how the UN Convention on the Law of the Non-Navigational Uses of International Watercourses has resolved this matter and rendered the two concepts reconcilable.

International practice, including international instruments and case law, confirms that states generally accept that they have a duty to provide prior notification of planned measures that may have a significant adverse effect upon co-riparians. The principle of “prior notification” is framed differently in various instruments, and it can broadly include the duty to “notify” and “consult” on planned measures. Prior notification helps to prevent and mitigate disputes, as underlined by the ICJ. Notification and consultation create the conditions for cooperation among riparian states and for ensuring the protection of international watercourses. On the contrary, the lack of notification and consultation may aggravate disputes as in the case of the Great Renaissance Dam along the Nile River. The UN Convention on the Law of the Non-Navigational Uses of International Watercourses (Watercourses Convention) provides a detailed procedural framework on prior notification and consultation. This essay outlines the established characteristics of the prior notification and consultation duty, then argues that the duty should be viewed not only as an inter-state obligation but also as including the obligation to inform and consult local communities.

The fundamental role of international law is to provide a framework for the coexistence of and cooperation among states. If international law and institutions work well, their contribution to the management of international affairs remains in the background. This essay seeks to illuminate the largely unnoticed work of river commissions in preventing and resolving cross-border water disputes. Among the oldest of international organizations, river commissions have long been at the forefront of technical and diplomatic interactions between countries. Similar to other international organizations, river commissions were created to better coordinate interstate interactions and more efficiently pursue common goals. They differ from other international organisations in the focus on water, a unique substance that cuts across so many aspects of human existence and requires specific treatment depending on the hydrological, political, social and economic context. Given the diversity of the contexts, river commissions differ from each other in their design and the tasks assigned to them. Therefore, a river commission is an umbrella term that encompasses a diversity of joint arrangements for cooperation between the riparian countries over their shared waters. This essay argues that river commissions helped to prevent, mitigate, and resolve many cross-border water disputes by building communities over water, enhancing technical knowledge and routinizing organisational transformations.

Quarrels between states sharing a transboundary aquifer (TBA) have been relatively minor in comparison with the more boisterous disputes seen in many of the world's shared river basins. Yet, transboundary groundwater can easily serve as the basis for cross-border disagreements. Twice as many TBAs and shared groundwater bodies have been identified globally as compared to transboundary rivers and lakes, and the volume of accessible groundwater exceeds all surface waters by a factor of one hundred. Yet, the number of treaties in force for TBAs is miniscule in comparison with those for transboundary rivers and lakes. Moreover, dozens of nations exploit groundwater from a TBA, often unilaterally and without knowing the cross-border implications, or even that the aquifer is transboundary. The lack of prioritization of groundwater in international practice and law, coupled with the reality that groundwater is “out of sight,” and thereby “out of mind,” has relegated shared aquifers as the neglected stepchildren of international water law. But, with many of the world's nations experiencing growing water scarcity and stress, this situation undoubtedly will change. This essay highlights the growing pains of international groundwater law and the challenges for its identification and articulation. Specific hydrogeologic characteristics of various TBAs are presented and, where relevant, placed in the context of water scarcity and security and recognized international legal norms.