Long-term future planning is not a new approach in urban water management (UWM). However, the conventional ‘stationary approach’ of infrastructure planning and decision-making, where the future is assumed as the continuation of historical observation, will not work in the rapidly changing environment. This is because the current and future change pressures, such as climate change, urbanisation, population growth, deterioration of infrastructure systems, and changes in socioeconomic conditions are always uncertain. Uncertainty in future change pressures stems from two quite different sources: incomplete knowledge and unknowable knowledge. Incomplete knowledge is due to lack of information and understanding of a system. Unknowable knowledge is due to the inherent indeterminacy of future human societies and both natural and built systems.