A hydraulic model of the network is used that describes the structural data and the laws governing the distributed flows. The model is fed with operational data relative to primary input parameters and, using the model, theoretical values are obtained for primary output parameters. The theoretical values are compared with measured values. In case of a significant deviation, the corresponding primary output parameter becomes a secondary input parameter in an inverse model including new secondary output parameters, which are added relative to the direct model and which correspond to primary input parameters. The secondary output parameters are, by priority, those to which the primary output parameter exhibiting the abnormal value is particularly sensitive. If necessary, the method is implemented iteratively by progressively restricting the number of the secondary output parameters.