Rethinking Urban Water Systems: Nearly Zero-Water Buildings and Urban Water Communities for Resilient Smart Cities

Urban water systems are increasingly challenged by climate change, population growth, and resource scarcity, requiring a shift from centralised, supply-oriented models to decentralised, resilience-based approaches. While energy transition policies have successfully promoted Nearly Zero-Energy Buildings (NZEB) and Renewable Energy Communities (REC), similar concepts for water management remain underdeveloped. This study proposes adapting these energy-based frameworks to the water sector through the concepts of Nearly Zero-Water Buildings (NZWB) and Urban Water Communities (UWC). A structured literature review is combined with a quantitative water balance analysis to evaluated the potential for reducing potable water demand through efficiency measures, greywater reuse, rainwater harvesting, and alternative local renewable sources. Results indicate that potable water consumption in residential buildings can be reduced by 53–100% depending on system configurations and local resources availability. Extending these strategies from building-scale solutions to district scale through water communities enhances system redundancy, flexibility, and adaptive capacity. The study further discusses the integration of decentralised water systems with smart city frameworks, highlighting the role of hybrid infrastructures in improving urban resilience. The findings demonstrate that decentralised and circular water strategies can play a key role in enabling sustainable, climate-adaptive, and smart urban environments, while also identifying regulatory and governance challenges for large-scale implementation.