Amid growing urban climate uncertainty and complex water demand, conventional standalone rainwater harvesting (RWH) systems often fail to ensure supply reliability and overflow control. Most existing studies focus on single-function building clusters, leaving a gap in understanding how functionally diverse groups with complementary demand patterns can be coordinated. This study addresses this gap by applying an hourly water balance model to compare decentralized and coordinated modes for an integrated RWH system serving a campus and adjacent student dormitories in Kitakyushu, Japan. Five performance metrics were evaluated: potable water supplementation, reliability, non-potable replacement rate, overflow volume, and overflow days. The results show that coordinated operation reduced annual potable supplementation by 14.1%, improved overall reliability to 81.7% (a 9.6% gain over decentralized operation), and increased the replacement rate to 87.9%. Overflow volume decreased by 295 m³ and overflow days by five, with pronounced benefits during summer rainfall peaks. Differential heatmaps further revealed distinct spatiotemporal advantages, though temporary disruptions occurred under extreme events. Overall, the study demonstrates that cross-functional coordination can enhance system resilience and operational stability, while highlighting the need for adaptive scheduling and real-time information systems for broader urban applications.

Green buildings, as highly efficient and energy-saving structures, aim to reduce reliance on conventional energy sources, lower carbon emissions, and enhance energy utilization by harnessing renewable resources like solar and wind energy. Photovoltaic-thermal systems and rainwater harvesting systems are pivotal sustainable infrastructures in green buildings. However, two critical factors impede the further enhancement of building energy efficiency. First, the overheating of photovoltaic-thermal (PVT) components reduces their conversion efficiency. Second, rainwater systems face water supply–demand mismatches. Furthermore, both systems compete for the limited space available on green roofs. The rainwater photovoltaic-thermal systems represent an emerging technology that integrates photovoltaic solar thermal systems with rainwater harvesting systems on building rooftops. This integration effectively addresses the overheating issue associated with PVT modules by designing rainwater pipes to circulate through the modules for cooling purposes. Additionally, the electricity generated by the photovoltaic panels powers the energy-intensive components of the rainwater systems. Meanwhile, the specific inclination angle of the photovoltaic panels enhances rainwater harvesting efficiency, thereby facilitating mutual resource utilization. This paper critically reviews the integrated rainwater photovoltaic-thermal systems to determine whether installing the coupled system on building rooftops is more energy-efficient than installing the two systems separately and whether it better supports the sustainable development of green buildings. By analyzing the independent opportunities and challenges of each system, this study concludes that the coupled system significantly contributes to improving building energy efficiency, reducing consumption, and advancing green building development.

Urban buildings stand as both a core source of carbon emissions and a key carrier of human settlements