London’s ability to remain a world-leading city in an increasingly globalised economy is dependent on it being an efficient, low-risk place to do business and a desirable place to live. However, increasing climate risk from flooding, overheating and water scarcity threatens this, creating the need for adaptation. An adaption pathway describes a structured sequence of adaptation decisions that are designed to manage climate risk in a wide range of possible future conditions. Analysis of sequential adaptation decision ‘pathways’ helps to demonstrate how climate risk can (or cannot) be managed, whilst retaining the flexibility to respond to future uncertainties. Whilst adaptive planning has gained increasing attention, the uptake of such methods has been relatively limited compared to the scale of the adaptation challenge due to institutional, financial and methodological barriers. This paper introduces a framework for adaptation planning in urban water supply systems that links existing risk-based decision-making with the development of long-term adaptation pathways. We present a quantified assessment of how the risk of water shortages in London is predicted to vary dynamically through to 2100 depending on the choice of adaptation pathways and under different long-term transient population and climate scenarios. This approach helps to reconcile multiple decision timescales and demonstrates the value of strategic long-term adaptation planning to stakeholders by outlining long-term futures that may influence medium-term decision-making. Adopting a flexible approach to adaptation will be critical to the management of risk under uncertainty. This adaptation pathways approach demonstrates an effective framework for informing such decision processes.