An Estimate for Optimum Capacity of a Rainwater Storage Tank Installed in an Individual House

Abstract

Considering the daily precipitation for 30 years in Matsuyama, the rainwater collection area, the city water charge system, and the installation subsidy, an optimum capacity of rainwater storage tank installed in an individual house is discussed. The rainwater stored in the tank is assumed to be used only for flushing toilet and watering plants, thus, no water quality concern is necessary. The obtained results showed that, generally, the capacity of the tank should be as big as possible to maximize the rainwater use. However, as the capacity of the tank increases beyond 2 m3, the increase rate of usable rainwater volume decreases. In addition to that, considering the recovery period of installation cost of the rainwater tank and the installation space required, it is concluded that the tank with a capacity between 1 and 2 m3 is most suitable for an individual house in Matsuyama. If there is enough space to install the rainwater tank, the 2 m3-capacity rainwater tank is recommended. Supposing all individual houses install the rainwater tank with a capacity of 2 m3, the water demand of Matsuyama City would be reduced by 17%.