Two intervention plans are considered to increase water supply. Firstly, desalination plants are built to supply twenty cities in addition. Minimum Spanning Tree is used to work out the optimal water transfer plan. Then, we design a plan that collection device is covered on the roof to collect rainfall. AR Model is established to predict the amount of rainfall considering the temperature and humidity. It can be used to flush the toilet, which can avoid water transportation. The amount of saved water is estimated.