Broad-scale, multi-governance level, participatory water management processes intended to aid collective decision making and learning are rarely initiated, designed, implemented, and managed by one person. These processes mostly emerge from some form of collective planning and organization activities because of the stakes, time, and budgets involved in their implementation. Despite the potential importance of these collective processes for managing complex water-related social–ecological systems, little research focusing on the project teams that design and organize participatory water management processes has ever been undertaken. We have begun to fill this gap by introducing and outlining the concept of a co-engineering process and examining how it impacts the processes and outcomes of participatory water management. We used a hybrid form of intervention research in two broad-scale, multi-governance level, participatory water management processes in Australia and Bulgaria to build insights into these co-engineering processes. We examined how divergent objectives and conflict in the project teams were negotiated, and the impacts of this co-engineering on the participatory water management processes. These investigations showed: (1) that language barriers may aid, rather than hinder, the process of stakeholder appropriation, collective learning and skills transferal related to the design and implementation of participatory water management processes; and (2) that diversity in co-engineering groups, if managed positively through collaborative work and integrative negotiations, can present opportunities and not just challenges for achieving a range of desired outcomes for participatory water management processes. A number of areas for future research on co-engineering participatory water management processes are also highlighted.