There is a pressing need to strengthen systemic integration and mutually supportive interpretation of norms and institutional coordination between the UNECE environmental agreements with a view to understanding their collective contribution to clarifying and further developing international water, environmental and general international law. This chapter identifies the contribution of the UNECE regime to established ‘central or cornerstone rules and principles’ of international water law, including the due diligence rule to avoid or mitigate transboundary harm, the duty to cooperate, the principle of equitable and reasonable use and transboundary environmental impact assessments (EIAs). Key findings demonstrate that these rules and principles are defined in greater detail in the UNECE treaties compared to global treaties, which fills gaps in international law. For example, the UNECE clarifies international law regarding transboundary EIAs by providing criteria to identify what level of risk triggers the obligation to conduct an EIA and compulsory minimum content of EIAs. The UNECE regime also clarifies the effect of applying general principles, like the precautionary and polluter pays principles to the ‘no harm’ rule which strengthens these obligations. The strengths and weaknesses of UNECE’s contribution to developing reporting mechanisms for the Sustainable Development Goals, especially SDG 6 on water, are discussed.

This chapter provides an understanding of where international law is at (including customary international law, treaty and case law) in terms of its achievements and shortcomings regarding cooperation over environmental protection and use of transboundary freshwater ecosystems. This work provides a basis for critical analysis over the proceeding book chapters, in relation to the value added by the UNECE. The chapter lays the foundations for determining the UNECE regime’s relationship to international water law, international environmental law and general international law. It explores the role of international courts and the international law commission in interpreting outdated water treaties and bringing their standards of environmental protection closer to contemporary scientific understandings and the more progressive multilateral environmental agreements in accordance with the principle of systemic integration. It also explores instances where Courts have arguably has not gone far enough, leaving gaps in understanding. Unlike Courts, pan-regional or basin treaties and their river basin commissions can develop and interpret rules and principles of international water law on a continual and comprehensive basis and provide the institutional framework which supports implementation and compliance with international water law. This hypothesis, on the added value of the UNECE water regime, is tested over the proceeding chapters.