By reviewing and blending two main bodies of research (critical transboundary water interaction analysis and centuries of thought on social justice) this paper seeks to improve international transboundary water interaction analysis and diplomacy. Various implications for transboundary analysis and diplomacy are grouped under themes of equitability, process/outcomes, and structural concerns. These include shortcomings of analysis and policy based on unfounded assumptions of equality, and options excluded from consideration by the legitimisation of particular concepts of justice over others. As power asymmetry is seen to enable or disable justice claims and conflict resolution efforts, the importance of ensuring equitable outcomes as a pre-condition for cooperation is asserted. Similarly, water conflict resolution is found to be more fair – procedurally – than is conflict management, and may be supported to a limited extent by international water law. A number of analytical tasks are suggested for future research and policy, including a call to scrutinise the source of legitimacy of strands of justice invoked. Given the very many perspectives on justice that exist in the network of relevant actors, potential bias in research and diplomacy could be reduced if all involved openly stated the morals underpinning their understanding of ‘justice’.