This paper deals with the design of flexible multiple plant water networks. Some practical features of multiple plant integration such as operating flexibility and expensive operating cost have made the number of cross plant interconnections (CPIs) an important parameter of water minimization problem. By combining pinch insight with mathematical programming, target freshwater usage and CPI conditions are obtained first without considering the detailed network design. Subsequently, an MILP model is established for the design of flexible water networks of individual plants. The proposed systematic approach can be applied for both fixed contaminant (FC) operations and fixed flow rate (FF) operations, limited to a single contaminant. An example from literature and a practical example of a chlor-alkali complex are used to illustrate the applicability of the approach.