Nowadays, due to the complexity of water distribution systems and their large scale, their design, operation and maintenance require the use of optimal methods, which have become more important than in the past in improving their calibration. The most important issue in the simulation modeling of these systems is the consistency between the calculated and measured data. In the absence of the results of unaccounted water studies in the network, the use of statistical experimental methods is still needed as one of the main elements in model calibration. Based on this, the current research was conducted to investigate the effects of different patterns of unaccounted water based on the calculated water consumption patterns and to determine the optimal pattern of unaccounted water within the water distribution network covering the number of 6 ground reservoirs. The comparison of the statistical parameters showed that the use of the inverse model of the customers' consumption, which is not considered as a water model, for calibrating the hydraulic model of the distribution network, provides more acceptable limits for the closeness of the predicted values to the recorded values of the hourly output of the reservoirs, and therefore It is better to be used in studies related to planning and designs.