In urban water distribution networks, as the age of the pipes increased, the rates of pipe breakage and water losses increased which causes financial losses to the water and sewerage company. Therefore, to reduce the number of breaks and leaks in pipes, worn pipes should be replaced. Replacing old pipes is an expensive and costly procedure. Thus, it may be more economical to replace the pipe at the appropriate time. In this research, the urban water supply network of Hamedan was simulated by

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... ng system dynamics approach. Then the optimal time for pipe replacement was estimated by using analytical solution of the net present value equation and the combined method of system dynamics-net present value. Also, in order to improve the financial balance of Hamadan Water and Sewerage Company, the optimal price of drinking water was determined by using the Powell optimization algorithm method. Dynamic simulation was performed in VENSIM. To test the model, the simulated data were compared with the observed data collected from the water and sewerage organization of Hamedan over the period 2014 to 2018. To statistical analysis and calculating statistical, the root mean square error, standard error and correlation coefficient (R2) were used. Base on the results, for the Benefit-Cost variable, the RMSE index was calculated to be 0.006, the SE to be 0.010 and the R2 to be 0.991. Comparison of the standard error showed that the difference between the observed and simulated values of the standard error of the Benefit-Cost variable is less than about one percent. The result indicate that the presented model has the very high accuracy. Base on the results of the study, the optimal time for pipe replacement is 2041. Finally, the results of this study show that the financial balance of the company can be increased by determining the optimal price of drinking water. However, the level of social welfare can be improved by increasing the renewal coefficient of pipes. Conclusion: Therefore, the system dynamics method and Powell algorit [...]