The practical application of the model of water supply network realized in the program Epanet 2 requires the calibration of the model. The proposed simple calibration procedure, allows for taking into account the changes in resistance caused by the aging process, to be substituted by resistance coefficient K. In order to determine the substitute resistance coefficient K, the fire hydrant flow tests could be used, which allows to determine the aging for a given material. Calibration of the water supply network model is shown on the example of a small urban network in central Poland..