Abstract
This paper develops the efficiency of rainwater usage system in detached dwelling by carrying out the numerical simulation with hourly water consumption and hourly rainfall in Fukuoka city, with considering water usage and human life cycle. From there, we indicate the beneficial efficiency of small rainwater usage system with showing the three rainwater usage efficiency indexes and one flood control index, the reduction number. Moreover, considering the relations among the four indexes, we show the rate of effective usage and the reduction number having the same content and the difference between the rate of alternation and the yield of cistern.,
