The calibration of a Water Distribution Network - WDN is defined as the adjustment of some parameters, looking for establishing a model which represents in the best way the field gathered data. The key variables considered in a typical WDN are the Unknown Demands (commercial losses), Emitters (technical losses), Diameters, Absolute Roughness and Minor Losses. The mass of water demanded by the system is mainly governed by Unknown Demands and Emitters. A network mostly characterized by one of those parameters cannot be calibrated through the other. According to this analysis, a mathematical procedure was defined to identify which of both problems is affecting a network. The methodology is based on the flow and pressure measurements of a network's zone.