Water diplomacy is regarded as a means to prevent conflict and to enhance peace through the cooperative management of transboundary water resources. There have been calls for water diplomacy to be given further attention, especially by foreign policy and security specialists, and to be extended to non-state actors through informal dialogue processes. The paper critically questions the qualitative changes water diplomacy delivers and argues for further analytical scrutiny on its efficacy. Using a critical hydropolitics perspective, the paper advances understanding of the way power asymmetries presiding over contested waters are altered or maintained, particularly through informal diplomacy. To exemplify, the paper uses Track 2 diplomacy or an informal dialogue process between non-state actors. Drawing on the case study of the Track 2 process by the Council for Security Cooperation in the Asia Pacific, the paper examines how foreign affairs experts deliberated water security in the Mekong river basin in the face of rapid dam development. The analysis demonstrates that information was forwarded to officials within the ministry of foreign affairs and created alternative knowledge channels, differentiated from networks of water and environmental ministries. Informal diplomacy also enabled downstream states, usually considered to have less influence on issues of water allocation, to exercise power in agenda-setting and influencing the debate. However, flows of finance around dam development within the region made it difficult for informal diplomacy to provide alternatives to existing transboundary water arrangements such that it changes power relations manifested in formal diplomacy. The paper suggests attentive analysis on the links between state and non-state actors through informal diplomacy and the nuanced way resources and networks are mobilised to control water resources.