On the contrary, cassava has the propotion of a higher rain water requirement than rice at 638 cubic meters in average. Nakhon Ratchasima is the largest area for cultivating cassava at 863 cubic meters, followed by Surin at 769 cubic meters, and Roi Et at 713 cubic meters respectively. Nevertheless, the data shows that rice has the propotion of the rain water requirement at 263 cubic meters in average. Maha Sarakham is the rice cultivating area which has the highest rain water requirement at 506 cubic meters, followed by Nakhon Ratchasima at 425 cubic meters, and Surin at 331 cubic meters respectively. However, according to the propotion of water requirement among 3 plants, it is found that palm has the highest water requirement, the irrigation water requirement at 6259 cubic meters and rain water requirement at 862 cubic meters.