Many countries such as Jordan are suffering from the problem of funding for infrastructure projects. This problem is very clear, especially, for the wastewater sewers and water pipes systems construction. The population of Jordan increased from five million in 2003 to ten million in 2017. Besides, the migration waves resulted in an increase in the population number in a short period of time. Under these circumstances Jordan must develop techniques and planes to build more efficient infrastructure projects. This issue was in focus by many governmental agencies, scientific workers, and engineers in order to find a successful methodology that take into consideration the high construction costs for sewerage systems. Therefore, this study is written to partially solve this problem and to find the optimum route of sewer system in cities. Jerash governorate is chosen as a case study because this city suffers from poor performance of the sewerage system. Finally, the total cost of the optimum system is calculated. In this study, the optimization methods is used to determine the optimal cost of sewer network that covers five municipalities of Jerash governorate. The integer linear programming is employed to developed and solve mathematical model equations with the h,elpful of using computer programs of WinQSB and MS-EXCEL program. The results showed that using optimization method is an efficient tool to find the optimum routes of sewer network system. The optimum routes of sewer systems is presented taking nto account the topography, population, fixed and variable costs. The total cost of the optimum route was found to be equal to (41,405,538) US$ US$ which means a reduction equal to 44%. The model is very efficient, as shown by sensitivity analysis in chapter four. The increase and decrease of the population values have the negligible effects on the calculation of total cost. This study could be adopted by the authorities responsible for the design of sewerage systems in Jordan. Also, it is expected that the results of the present work can contribute to optimize an integral model for optimizing a total regional wastewater treatment plants.