Hydraulic analysis methods of water distribution networks are divided into two types of demand driven simulation method (DDSM) and pressure driven simulation method (PDSM). In the DDSM analysis, it is assumed that nodal discharge is independent from nodal pressure and available discharge is always equal to demanded flow at consumption nodes. In PDSM analysis which results in much more realistic outputs than DDSM method, the assumption of nodal discharge independency from nodal pressure is rejected. In the recently proposed pressure-dependent relations, nodal discharge has been divided into two sections of volumetric and pressure-dependent discharges. In these relations, the exact contribution of volumetric and pressure-dependent discharges is not known and a portion of 50% has been considered for each of them. In the present study, by implementing field measurements, the portions of volumetric and pressure-dependent drinking water consumptions have been determined and the pressure-discharge relationship has been modified. Then, impact of the modification applied on pressure-discharge relationship on the output of PDSM model has been investigated. According to the obtained results, the considered portions for volumetric and pressure-dependent consumptions (50%) in previous pressure-discharge relations are inconsistent with reality. Using the modified pressure-discharge relation leads to increase in tank outlet discharge in the hydraulic model. Volumetric and pressure-dependent consumptions in cities like Oshnaviyeh can be considered approximately 13 and 87% of total drinking water consumption, respectively.