An analytic hierarchy process for assessing externalities in water leakage management

Abstract

One of the main challenges that water supply managers face is that of minimizing the water lost through leakage from the systems that they operate. To minimize water losses, substantial amounts of money must be invested every year in leak detection and repairs. This investment is usually balanced by the benefits derived from the use of the recovered water. Nevertheless, this scheme of economic assessment does not reflect the whole dimension of the profit-earning capacity of repairing leaks; and the associated benefits go beyond just the economic value of the recovered water. In this paper, we consider a new economic assessment approach that includes all the costs incurred by the existence of leaks and the benefits derived from their control. The main difficulty derives from the fact that comparisons with regard to certain properties will only work for properties with well-defined scales of measurement. The analytic hierarchy process of Saaty (2008) [1] provides a useful way to establish relative scales that are derived by making pairwise comparisons using numerical judgments from an absolute scale of numbers. The unique largest eigenvalue and the Perron eigenvector of the matrix of criteria provide, taking into account the properties that this matrix exhibits, the necessary information for dealing with complex decisions that involve dependence and feedback. These decisions are analyzed in the context of benefits, opportunities, costs, and risks. We also present a method for improving the consistency of the comparisons — as consistency may be affected by subjectivity. The main conclusion is that water supply managers and authorities should shift direction from purely economic policies based on passive leakage control towards new social and environmental policies that consider more proactive actions.