We reflect on methodologies to support integrated river basin planning for the Ayeyarwady Basin in Myanmar, and the Kamala Basin in Nepal, to which we contributed from 2017 to 2019. The principles of Integrated Water Resources Management have been promoted across states and regions with markedly different biophysical and political economic conditions. IWRM-based river basin planning is complex, resource intensive, and aspirational. It deserves scrutiny to improve process and outcome legitimacy. We focus on the value of co-production and deliberation in IWRM. Among our findings: (i) multi-stakeholder participation can be complicated by competition between actors for resources and legitimacy; (ii) despite such challenges, multi-stakeholder deliberative approaches can empower actors and can be an effective means for co-producing knowledge; (iii) tensions between (rational choice and co-productive) models of decision complicate participatory deliberative planning. Our experience suggests that a commitment to co-productive decision-making fosters socially legitimate IWRM outcomes.