Abstract: Water system integration，which treats the water utilization processes in an enterprise as an organic whole to consider how to allocate water in a water system，shows remarkable effectiveness in saving water. In this paper，three technologies for water system integration in recent years，including pinch technology，mathematical programming and the integration with internal water mains，are analyzed. The advantages and disadvantages of each method are demonstrated and an example is used to compare these methods. Finally the future development of the methods for water system integration is discussed.