The main interest of the methodology for the investigation of wastewater reclamation and reuse systems which is proposed in this paper is that all costs and benefits (social and private) are considered in the economic and technological analysis. This general concern allows an improvement in the design of investment decisions. Traditionally, an economic-financial analysis of wastewater reclamation and reuse systems focuses exclusively on the study of costs and private benefits. The methodology that is presented in this paper takes into account not only the private impacts but also the project spillovers which could have relevance on the project. In this research, the use value of the reclaimed water in the Natural Wildlife Park of Aiguamolls de l’Emporda` is estimated. The travel cost technique is applied to estimate the external value of the Park. According to the final results, the price of the reclaimed water in the Park should have to be between 0.75 ⁄/m3 (without opportunity cost) and 1.20 ⁄/m3(with opportunity cost).