Water resource management should be made from a multidisciplinary perspective. In this sense, economic research into the design and implementation of policies for the efficient management of water resources has been emphasized by the European Water Framework Directive (WFD). Cost–benefit analysis (CBA) is one of the more widely accepted economic instruments since it is a rational and systematic decision-making support tool. Moreover, the wastewater treatment process has significant associated environmental benefits. However, these benefits are often left uncalculated because they have no market value. In this paper, using the concept of shadow price, a quantification of the environmental benefits derived from wastewater treatment is made. Once the environmental benefits are estimated and the economic costs of the treatment processes are known, a CBA is made for each of the wastewater treatment plants (WWTPs) under study. In this way, a useful economic feasibility indicator is obtained for WWTP operation.
