The search for suitable segmentations is a challenging issue for analysis, planning and management of water distribution networks (WDNs). In fact complex and large size hydraulic systems require the division into modules in order to simplify the analysis and the management tasks. In complex network theory, modularity index was proposed as a measure of the strength of the network division into communities. Nevertheless, modularity index needs to be revised considering the specificity of the hydraulic systems. Accordingly, the classic modularity index is firstly presented and, then, tailored and modified for WDNs. Furthermore, a multi-objective strategy for optimal segmentation is presented. The optimization framework is based on the maximization of the WDN-oriented modularity-based index versus the minimization of the cost of newly installed devices in order to segment WDNs