Combined Sewer Overflows (CSOs) prevent property flooding, but increasingly extreme weather, urbanisation, and population growth are causing more frequent spills. Rising environmental pollution concerns have intensified regulatory and public scrutiny. Sustainable urban drainage systems (SuDS) are a proven method to reduce CSO spills; however, uncertainty around sewer network connectivity often leads to SuDS investment decisions being made without sufficient data for robust cost–benefit analysis or optimal site selection. Yorkshire Water and BMA collaborated to use advanced cloud technology to develop a simplified Digital Business Twin (DBT) for three catchments. The DBT was validated using four years of rainfall data and CSO event duration monitoring, achieving 77.4% spill prediction accuracy. It was then applied to test 160 scenarios incorporating varying rainfall forecasts, climate change impacts, budgets, and SuDS implementation costs. High resolution catchment maps were created to visualise property level investment rankings based on budget, predicted spill reduction, and the most suitable SuDS intervention (e.g., water butts).Results showed that in the most urban catchment, an unconstrained budget could deliver an average CSO spill reduction of up to 87.4%. The approach also demonstrated the added value of SuDS in lowering treatment and pumping costs through surface water separation.