Water reuse is an emerging and promising non-conventional water resource. Feasibility studies are
essential tools in the decision making process for the implementation of water-reuse projects. However,
the methods used to assess economic feasibility tend to focus on internal costs, while external impacts
are relegated to unsubstantiated statements about the advantages of water reuse. Using the concept of
shadow prices for undesirable outputs of water reclamation, the current study developed a theoretical
methodology to assess internal and external economic impacts. The proposed methodological approach
is applied to 13 wastewater treatment plants in the Valencia region of Spain that reuse effluent for
environmental purposes. Internal benefit analyses indicated that only a proportion of projects were
economically viable, while when external benefits are incorporated all projects were economically
viable. In conclusion, the economic feasibility assessments of water-reuse projects should quantitatively
evaluate economic, environmental and resource availability.
