Effective transboundary water cooperation requires enforceable coherent legal frameworks. Implementing the rules of international law that apply in a domestic context presents considerable challenges. This paper examines some of the issues in this scenario through the case study of Lao PDR. After setting forth the key rules that apply in this field, the study examines the historical context within which to explore the evolution of national implementation of equitable and reasonable utilisation in the Lao PDR case study. The work concludes with observations on how this offers insights into the broader challenges in this area.