This paper focuses on the simultaneous optimization of the heat-integrated water allocation networks. Amathematic model is established to illustrate the modified state-space representation of this problem. An easy logicalmethod is employed to help identify the streams of hot or cold ones. In this model, the water exchange networks (WEN),heat exchange networks (HEN), and the interactions between the WEN and HEN combine together as one unity. Thus,the whole network can be solved at one time, which enhances the possibility to get a global optimal result. Examplesfrom the literature and a PVC plant are analyzed to illustrate the accuracy and applicability of this method.