## 3 Model and Application
### Application of the Model to a Case Study
These criticalities, which characterize the specific portion of the territory served by the utility, were selected from the set of criticalities {CA} that the EGA identified for the entire ATO (a supra-municipal geographical area that can be served by several utilities). In turn, the set {CA} is deduced from the general scheme of criticalities {C}, prepared by the ARERA and valid at the national level, which defines all the potential problems that may concern the IWSM. The criticalities of the set {C} (initially introduced by the ARERA with resolution 3/2014 DISD, then increased in number and partially modified with resolutions 2/2026 DISD and 1/2018 DISD) have been classified by the authority into areas and subareas. This classification can therefore also be applied to the {CA} and {CT} subsets. To identify the {CT} criticalities, the utility, supervised by the EGA, carried out a complete survey of the water infrastructures, as well as sewage and purification systems, assessing their technical quality through a series of indicators introduced by the ARERA with resolution 917/2017/R/Idr. Furthermore, feedback was collected on the degree of user satisfaction with the service offered. It was therefore possible to evaluate the contractual quality through a series of indicators introduced by the ARERA with resolution 655/2015/R/Idr. For further and more detailed information about the criticality selection and measurement processes {CT}, which are described in Phase 1 of the protocol of Figure 1, the reader can refer to the previous study published by the authors [20]. Compared to Phase 1, the authors carried out consultancy activities directing the utility in data collection and providing assistance regarding the correct interpretation of the technical and contractual quality indicators. Figure 3: Comparative hierarchy for the investment program. The investments to be ranked according to the time priority of implementation were identified, analyzed and selected in Phase 2. In this phase, the water operator presented a proposal for intervention consisting of a series of design alternatives to the EGA for each criticality to be mitigated. In Subphase 2\({}_{2}\), the best design alternative (a\({}_{\text{Mi}}\)) was selected for each criticality, therefore, for each group of design alternatives. Downstream of this selection process, the 11 design alternatives considered the best were identified, as shown in Table 2. The selected alternatives can contribute to reducing more criticalities. For more information on the identification of design alternatives and on the process of selecting the best alternatives through the AHP (Phase 2 of the protocol of Figure 1), the reader can refer to the previous study published by the authors [20]. However, it is useful to underline that, for the preliminary definition of the set of alternatives proposed for each criticality, we used a consultancy of engineers and civil companies specialized, respectively, in the design and construction/maintenance of hydraulic infrastructures. Instead, the authors of this study dealt with the estimation of investment and maintenance costs for each project alternative. Furthermore, we dealt with the definition of the financial criteria to be considered for the implementation of the AHP.