Towards integrated sustainable urban drainage and greywater reuse systems: A conceptual framework based on hybridisation

Sustainable Urban Drainage Systems (SUDS) and Greywater Reuse Systems (GWRS) are increasingly promoted to address water scarcity and flood risks in arid/semi-arid cities, yet they are typically implemented independently. This study proposes a hybrid configuration combining SUDS with GWRS and assesses its feasibility. A systematic literature review identified the main challenges of standalone systems in arid contexts, a convergence matrix classified the cross-system interactions, and a causal loop analysis explored how key interactions propagate over time and influence system-level behaviour. Results show dense interactions between SUDS and GWRS challenges, reflecting both mitigation opportunities and integration risks. Hybridisation reduces seasonal SUDS inactivity, improves land-use efficiency, and enhances monitoring capacity, while creating additional technical and governance requirements. Whereas reinforcing feedback strengthens the reliability and institutional support, balancing feedback relates to complexity and cost constrained expansion. Overall, hybrid SUDS-GWRS systems offer advantages when supported by coordinated governance and long-term management.