Water utilities must provide sanitation services using ageing infrastructure originally designed for historic climate, regulatory, and population-flow conditions that no longer apply. As a result, many wastewater treatment works (WWTWs) require investment to increase capacity and treatment capability. In dense urban areas, however, expanding existing WWTWs is often impossible due to space constraints, as seen in the Dalmuir Catchment in Scotland. This challenge drives the need to redirect flows and create sub catchments served by WWTWs that are fit for purpose while meeting budget, geographic, and network design constraints. BMA and Scottish Water have collaborated to develop a simplified Digital Business Twin (DBT) of the Dalmuir Catchment using advanced cloud technology. This enables a systems planning approach where the cost and value of multiple sub catchment configurations can be assessed through mass scenario analysis across varied rainfall, climate change projections, and WWTW operational expenditure conditions. Initial results assessed five catchment configurations across three time horizons (2030, 2050, and 2070). The analysis identified an optimal reconfiguration that reduces full flow to the existing WWTWs by 60% and decreases spilling days by up to 94%. This tool supports adaptive, whole systems planning by quantifying trade offs across future scenarios and identifying least regret options for catchment configuration.