In this study, we developed the assessment method that evaluate the water demand management and calculate the water saving volume using water use indicator, and developed the system to link the water saving volume that occur through demand management and water supply and demand. The results from this study, local governments with poor water conditions should be followed to improve the water supply. And, future water demand estimates should be even considering it. We calculated the water saving volume of the Geum River basin using K-WEAP (Korea-Water Evaluation And Planning System) and performed the water budget analysis. We found that the change of river flow, ground water level and reservoir water level, and it can be utilized for other demand.