This paper studied on the potential utilization quantity and some regional comparisons for designing the rainfall cistern systems by the basic analysis of the characteristics of daily rainfall data of remote islands in Japan.
At first, some references were made to show the relations between the annual rainwater depth and the scale, the structure and many problems for maintaining and improving the water quality.
Secondly, the basic analysis was made on the daily rainfall data in the remote islands islands in Seto Inland Sea where water supply condition has been so severe and the data in Maizuru was added for comparison, where annual precipitation depth is near the average value of all Japan.
Here the potential maximum utilization of cistern system with roof (100 m^2 ) catchment system in the districts were estimated from the average annual precipitations from long terms as over 10 years. And the characteristics of the frequency distributions of daily rainfall and the continuous no rain days have proved that those effect so much on the desing the system. And simulation of cistern store with daily rainfall showed the needed the storage volume of the cistern tank and supplementaly water volume to maintain the stable water supply in the cictern system.