Research Programs


Rooftop Rain Catchment Sizing

WERI On-line Publication:
Designing Your Rainwater Catchment and Storage System »

The two major sources of water supply in the atoll islands and many rural areas of the high islands of the Federated States of Micronesia (F.S.M.) are rooftop rainfall catchment systems (RRCS) and shallow groundwater sources. The rain catchment systems are best suited for supplying drinking water needs. Other water demands are best met from groundwater sources. An ideal water supply system would have the components of the RRCS and the groundwater components sized in such a manner to meet the needs of the individual family that owns the system.

This project, which was funded by the US. Geological Survey Water Institute Program, was designed to develop and disseminate criteria to be used in the design of new or refurbishing of existing individual water supply systems for various islands in the F.S.M. The end product was a design brochure for sizing combined rooftop rain catchment systems so that they can provide a continuous water supply even during drought conditions.

A Windows based computer simulation model was developed to evaluate the effectiveness of various RRCS configurations for varied use rates. The next phase of the study involved an inventory of use rates, catchment sizes and tank configurations for various island groups in the Federated States of Micronesia. This was used to update and verify past studies which have been made concerning water consumption in Micronesia. Rainfall data and use rates served as input to the RRCS model. Output from the model was used to develop a set of design tables to be used by island sanitarians and residents in planning the design of new or the upgrading of existing RRCS systems. A brochure containing these tables has been printed and is being distributed to Island residents in the Federated States of Micronesia. Several workshops have been held in F.S.M. so that local sanitarians and water resources planning personel can take full advantage of the brochure and computer program.

This first study developed guidelines for all the islands of Yap, State F.S.M. and all the islands of Namonweito Atoll and the Pattiw area of Chuuk State F.S.M. Other studies are presently being planned for Saipan in the Commonwealth of the Nothern Mariana's Islands, Pohnpei Island and Majuro and Kwajalein atolls in the Republic of the Marshall Islands.

For More Information on Rooftop Rain Catchment send e-mail to:
Dr. Leroy F. Heitz P.E.: lheitz(weri) Rain Catchment Sizing -

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