Water security issues arising from the Central Asian states’ heavy reliance on, and competition over, the shared waters of the Aral Sea Basin have attracted urgent political and academic discussion. However, any analysis of the role that international law plays in addressing these substantive complex problems remains incomplete and imprecise. This article sets the stage for a deeper understanding of international law and of its potential operation in the context of the transboundary waters in the Aral Sea Basin. It seeks to explore the substantive norms operating in the field, namely, the rule of equitable and reasonable use, the no-harm rule, and obligations relating to environmental protection, with a view to understanding how these substantive norms work and ascertaining what conduct is required of the states with respect to their shared watercourses.