The purpose of this study is to make clear the fluctuations of water balance and BOD-loading in development areas, where the changing conditions of building's composition and the combination of water reuse systems and rainwater treatment systems. The simulation program, including monthly and weekly fluctuations, is developed to evaluate the fluctuations of water reuse systems. After this, case studies are conducted using this program. The results are as follows. Water reuse systems have large fluctuations when using rainwater treatment system. The fluctuations are leveled where office buildings and hotels exist in the ratio of 40:60 in development areas.
