This paper deals with the competing promises of future prosperity that animate water-related development projects in contemporary rural Yunnan. Water Users’ Associations (WUA) have been garnering international attention as a cost-effective solution for growth-compatible sustainability in a water sector increasingly challenged by scarcity. These associations are inspired by Elinor Ostrom’s design principles for the management of common resources. This paper challenges the notion that the implementation of Ostrom-inspired WUAs in the Chinese countryside is fulfilling the associations’ accompanying promises of sustainable growth. Instead, it argues that Chinese WUAs proliferate thanks to pre-existing promises of collective prosperity. The paper brings into view the epistemic work that, through their repeated breaking, diverging promises of future prosperity perform in the Chinese water sector. North East Yunnan is rich in social arrangements for sustainable water management that predate the introduction of WUAs and make their ordinary operations possible. WUAs proponents conveniently blame the failure they see in Ostrom-inspired organisations on said arrangements, while retaining faith in Ostrom’s design principles. An ethnography of Ostrom-inspired associations can salvage Ostrom’s work from the prescriptive readings of development planners. Yet, it also shows that difference in human projects for the environment becomes implausible once captured by planners’ nomothetic episteme.