Abstract: A method based on non-linear programming is proposed to optimize water network in batch chemical processes with a single contaminant. An intermediate tank is used to receive the discharge water from each process and provide water to operations in batch processes，which increased reuse of process discharge streams. By pre-ordering the operations with discharge time from earlier to later，and combining with other heuristic rules，a superstructure of water network was constructed and simplified. The corresponding mathematic model involved a set of nonlinear equations is solved by the GAMS (general algebra model system) software tool. This method could achieve minimal fresh water use and optimal network assignments simultaneously. The results of a case study show that the method was effective.