Governing transboundary waters is inherently a complex policy issue. However, when waters flow through multiple urban spaces (multiple cities in different countries), it presents a unique challenge to access and control. Policy actors employ a variety of policy instruments to govern such spaces and users’ water demands. Drawing from the case of Geneva Metropolis (shared between Switzerland and France), we explain how policy instruments are formulated to manage a combination of water sources. We answer two questions: (1) what type of policy instruments contribute to reaching transboundary water governance in Greater Geneva? and (2) What are the underlying drivers that led to the success or failures of implementing policy instruments at the transboundary level? Based on policy documents and closed-door interviews, we present various policy instruments that have been developed and implemented in the Geneva metropolis. We further argue that the underlying drivers, such as the existence of communities of practice, political willingness, the influence of civil society actors and the evolution of an anticipatory water governance system, have influenced the policy instruments’ success and failure. To conclude, this article calls for further research on comparing different cross-border metropolitan areas, focusing on processual aspects (development and implementation) of policy instruments.