Water losses in water distribution systems represent one of the biggest problems facing a supply water company. To address this problem various actions should be taken that involve the investment of substantial resources. To invest more efficiently a suitable evaluation of alternative courses of action should be available.

The dynamic nature of a water supply company requires that managers must make decisions based on information available, and many times using the experience they have acquired throughout their life as well.

To this situation, we have to add the fact that to get sound management of leakage, managers must consider not only technical criteria, but additionally must be aware of social and environmental criteria. That is, they have to deal not only with tangible but also with intangible criteria. Moreover, even though some of these criteria may be easily translated into monetary units, there are others whose conversion is more difficult or downright impossible or inappropriate.

Thus, in order to make a decision regarding the policy to follow a water company must first be aware of its current state, including knowledge of externalities incurred in the implementation of its current work. Then, it is necessary to carry out a project evaluation to define a project economically viable for the company. From this point, the manager of the company or its staff should analyze the problems to solve and evaluate alternative solutions.

The starting point is the assumption that the company recognizes its position and has carried out a study to define an economically viable project. However, given that most evaluations concentrate efforts on technical and economic analyses, regularly criteria related to external costs and benefits incurred by the company are ignored, especially because they sometimes consist of intangibles or just of issues of difficult assessment.

The project development is a complex process, which needs time and effort. As a consequence, the transformation of all the elements to consider in comparable units is extremely complex; the more detailed assessment, the greater the effort required and the higher the cost of the project approach.

However, to make the right decision, the one which is closer to the reality of the supply company, the supply network, the users and the environment, as many elements as possible among those that make up the problem of leakage and management must be consider.

It is worth taking into account (and making use of) the knowledge and experience of supply managers and people working in the supply companies to address the lack of accurate economic valuation of some of the factors inherent to various problems about management of supply networks. Firstly, because they are responsible for making decisions; secondly, because they are the ones who know the reality of the organism and its infrastructure; and, thirdly, because drawing on their experience is not an extra cost in making decisions. 

This work has been developed to carry out this process. It consists of seven chapters, whose content and scope are briefly mentioned next.

Chapter 1 discusses issues related to water leakage in water distribution networks. Various flow estimation methodologies of lost flowrates are discussed. Also, the concept of economic level of leakage is addressed, which underlines the balance that companies should achieve between the resources invested to minimize water losses and the value of recovered water through the investment of these resources.

Chapter 2 consists of a description of various alternatives for leakage management, various approaches of management strategies, and the possibilities of setting targets for minimizing water losses.

Under the impact on the users and the environment generated by the work of the companies distributing drinking water, in Chapter 3 a description of externalities (benefits and costs) incurred by the leakage and management is presented. With the purpose of including leakage in the project evaluation and decision making, this chapter offers a description of the available options; we analyze the most appropriate methodologies, and finally opt for the use of AHP methodology.

Chapter 4 describes the AHP methodology; also some applications found in the literature are mentioned. Then we analyze the construction of pairwise comparison matrices of elements, describe the characteristics of these matrices, set the properties of consistent matrices, emphasise the need to improve consistency (if necessary) to validate the decision-making process, and, with this aim, we develop various alternatives to improve consistency that solve the most common problems of the AHP methodology.

Chapter 5 explains the overall process of decision-making, and various decision-making models are analysed. Here, we describe the computer application developed to automate the process of making policy decisions regarding management of leaks, which include social, environmental and CO2 emissions costs.

Chapter 6 presents twelve applications that validate the methodology, including options for improving consistency. These applications have served to approach real-world companies by conducting meetings with experts in distribution management, leakage and water projects. These experiences have helped to observe first-hand the situation of some supply companies, as well as to use the knowledge and experience of people who know the area, and to check the modest consideration of externalities in the assessment of leakage and alternatives management, not because of lack of interest, but because of the complexity of the task. Experts were presented with the AHP methodology, and the results have been satisfactory, because thanks to this methodology they are given the possibility of including not only the criteria for the externalities of leaks and their management in decision-making, but those defined during the approach to the problem.

Finally, in Chapter 7 the results obtained are presented. We also synthesize the conclusions reached after performing this work. Additionally, facing future research, various options to be developed in further research lines have been addressed.