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• Political decisions and support for experimentation to solve socio-environmental problems have potentials to provide innovative solutions. • Small-scale projects combining urban drainage and rainwater harvesting are possible in the built environment and suited to dense areas as well. • Urban planners rather than water planners may be able to push forward for sustainable drainage projects. • Planning for blue-green infrastructure opens windows of opportunity towards urban sustainability to multiple urban challenges. • Urban rain and urban drainage should be considered a resource and not a hazard. A plethora of socioenvironmental issues, and growing concerns over the effects of climate change, are forcing cities to rethink conventional urban water management practices. However, change towards more sustainable practices has been remarkably slow. This paper examines two cases of greening projects aimed at urban rehabilitation in Stockholm and Barcelona, which have turned into examples of innovative approaches to urban rain management. Both cities share high densities and flooding problems in certain neighborhoods. Specifically, the paper attempts to answer three questions: 1) what were the driving forces and key factors that facilitated the breakthrough of urban rainwater-harvesting (URH) schemes based on the two cases?; 2) who were the actors involved and what were their roles in moving towards URH schemes?; and 3) how can URH schemes become part of multifunctional, sustainable urban systems? To answer these questions, the paper uses concepts of adaptive context and capacity, and of actor agency, drawn from the transitions literature, and opportunistic and guided flexibility planning drawn from the planning literature. Empirical material for both case studies was obtained from policy documents and semi-structured interviews with key actors. The main results show first political support for flexibility in public planning, the adaptive context and the capacity of the actors, especially in taking advantage of windows of opportunity for the materialisation of new ideas. Second, the design and implementation of these systems widened the number and scope of actors in urban water management, incorporating new professionals such as architects and involving more city agencies and organizations. Third, small scale URH systems contributed not only to control urban drainage but performed other functions such as the much-needed greening of dense areas in both cities. [ABSTRACT FROM AUTHOR]