Abstract
In this paper, we describe the environment of domestic water systems, the people's opinions and the ways of water uses at Tonaki, Kitadaito and Izena island in Okinawa. And we analyse the suitable scale of equipments for rain water uses at Kitadaito island, using the simulation method. The main contents are as follows. At the islands with no tap water systems, the domestic water depends on well water and rain water in each house, and the well water influenced by the sea water and the sewage is restricted for using. At Tonaki island, mainly depended on well water, the rain water has been used for drinking. The other hand, at the island such as Kitadaito island, mainly depended on rain water for all uses in domesticities, the equipments for rain water using system so as the storage tanks are large in scale, and there are different ways of water uses as people's opinions for water conservation are high level in comparison to Tonaki island. Depended on the simulation results for using of rain water to Kitadaito island, it is showed that the usable amounts of rain water are the range between 600 and 700 (1/house, day) in many houses. We clarify the relation between catchment area (A) and storage tank capacity (B) for rain water collection system, and show that the effective ratio of (A) to (B) is at about 2 (m^2/m^3). The ratios in many houses are approximate to this value in Kitadaito island.
