Nature-based solutions (NBS) are recognised as cost-effective tools to alleviate pressure during high rainfall events while producing wider societal and environmental benefits, but uptake is limited in practice due to lacking evidence. The NICHES project – Nature's Integration in Cities' Hydrologies, Ecologies and Societies – aims to fill this gap by adopting a holistic social-ecological-technical systems (SETS) approach to explore the potential of urban NBS as an alternative to the costly renewal of grey wastewater systems. Five global cities – Barcelona, Berlin, Boston, Sheffield, and Rotterdam – will be utilized to co-create knowledge and develop a shared understanding of restorative NBS that can be applied to avoid storm-water run-off and negative impacts for aquatic biodiversity.