In this study, a new methodology based on performance indices is presented to carry out a detailed energy audit of water systems. Given a water network, the proposed procedure allows for a direct assessment of the critical areas in terms of energy efficiency, as well as for a detailed quantification of the energy benefits resulting from the new management strategies proposed to increase the sustainability of the network. To verify the viability of the methodology, a pressure control strategy is proposed, based on the installation of pressure-reducing valves, containing the excess pressure and thus the water leakage within the system. The operation strategy is carefully designed by the use of a global optimization solver, searching for both the number and location of the devices in order to maximize water savings and minimize the investment cost. The energy benefits resulting from the pressure control are then investigated by the assessment of the performance indices. According to the obtained results, the proposed methodology is a useful tool to assess the vulnerability and inefficiency of a given network, as well as to quantify the benefits resulting from the new management strategies.