Rainwater harvesting (RWH) is one the most salient methods in urban water management for creating an additional water supply in times of drought and combating urban floods in the face of climate change. Instalment of RWH systems has become compulsory by national legislation in Türkiye since 2021. However, previous research shows that there are a variety of barriers to implementing RWH, including legislative regulations, technical dimensions, financial mechanisms, societal adaptation and governance dynamics. Taking this as a point of departure, this research explores necessary actions to overcome those barriers in collaboration with relevant actors, aiming to catalyse the realisation of RWH systems throughout the research process. The research adopts a participatory action research (PAR) methodology, generating knowledge that is meaningful for urban planning systems and water management institutions involved in RWH installation and operation. The research explores the necessary actions through the case of Istanbul, the largest metropolis of Türkiye. Respectively, a set of workshops, focus groups, in-depth interviews, and group meetings were implemented in parallel processes with different actors from the public and private institutions at local, regional, and national scales. The findings highlight the need for (i) legislative actions for constructing a thorough regulatory framework, (ii) financial actions for introducing new incentives and pricing policies, (iii) technical actions for developing installation and operation standards, (iv) societal actions for igniting a cultural change for the use of RWH in the society and (v) governance actions for RWH systems. The research establishes a communicative environment that showcases the feasibility of collaboration and emphasizes the importance of its continuous implementation in establishing a decentralised governance mechanism involving all actors.