This paper presents a mixed-integer non linear programming model for the optimal design of integral cooling water systems. The model includes a superstructure for the HEN component of the system that allows arrangements of coolers in series and/or in parallel, and also allows the bypass of fresh water and/or previously-used water to improve the performance of the cooling network. The optimization of HEN coolers is made simultaneously to take into consideration from the synthesis stage the interactions between the pumping effects and the heat transfer coefficients that determine their transfer areas. The model considers as objective function the minimization of the capital costs for the cooling tower, HEN coolers and pumps, as well as the operating costs due to the fan of the tower, pumping requirements and water makeup. Three example problems are presented to show the application of the proposed method.