The shortage of water resources is high on the agenda of many countries. Despite its reputation for rain, the UK is not an exception, and particularly in the South East of England where high population (more than 19 million people) places a great burden on the water supply.

As a regulatory requirement, every 5 years water companies in England and Wales must produce plans on how they will meet their future demand. The plans must follow the “Economics of Balancing Supply and Demand” framework, and models are used to optimise the option investment to achieve the needed increase in water supply capacity. Water Resources in the South East (WRSE) is an alliance of the six water companies in South East England as well as the Environment Agency, Ofwat, the Consumer Council for Water, Natural England and Defra. WRSE’s aim was “to develop an affordable, sustainable and resilient regional approach to water resource management”, which would support the water companies in their planning.

This is a complex problem with potentially very large supply-demand deficits. Because of the long planning horizon, the uncertainties in climate, population and legislative drivers are significant. There is a need to optimise against this uncertain future to produce resilient plans. Previously, the main focus had been on identifying the least cost plan that met demand – a relatively straightforward optimisation problem. But being able to produce plans that are resilient and adaptable to uncertain events decades in the future and also incorporate other performance metrics (environmental benefit, customer preference and more) is a major technical challenge. How can we plan 75 years ahead for such a complex problem and with so many uncertainties?

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