Abstract
Unlike many structuring projects, treated wastewater reuse projects are rarely subjected to economic analysis. And when they are, the social and environmental benefits and costs are often not accounted for or are not properly quantified. Here we show that the widely used cost–benefit analysis method showing the profitability of a project from the whole of the community's point of view can be adapted to treated wastewater reuse projects. The remaining evaluation difficulties are more due to the system's complexity rather than its methodological limits. Indeed, the operator must be able to understand, formalize and imagine constraints and risks associated with different domains such as urbanism, agriculture, climate, hydrology and trade. Remaining uncertainties over key parameter values can, however, be properly considered through scenarios and/or stochastic approaches. We illustrate the implementation of this methodological approach with two case studies: Clermont‐Ferrand where treated wastewater is reused by a collective irrigation network; and Cannes where surface and groundwater recharge can enable indirect reuse for multiple purposes including indirect potable water production. These two French case studies highlight how economic analysis, dealing with uncertainties, can support decision making. Copyright © 2020 John Wiley & Sons, Ltd.