Indonesia has abundant of water from rainfall as indicated by a range of annual rainfall of 1400-5000 mm in comparison with Holland (750 mm), Iraq (200 mm). However, its potential evapotranspiration rates are very high in the range of 800 mm (in mountain regions)to 1300 mm (in very dry areas) in comparison to Holland (400 mm) but almost the same with Iraq. Since actual evapotranspiration depends very much on availabel of water to be transfered into vapour, consequently P-Eact for Indonesia on annual basis (example figures from upper Citarum river Basin)
is 2514-1258 mm=1256 mm, and for Holland is 350 mm and for Iraq is almost 0 mm. Study on theses facts, in case the actual evapotranspiration can be deleted from calculation by any means then more water can be conserved for full utilization by man. On regional basis it is impossible to do it, however, on small scale such haousehold scale this thing almost can be done. Water from rainfall is collected through gutter then flows into a reservoir which is completely to be closed for one reason to another. Losses due to evaporation which depends on the type of rooftop of buildings is very small and consequently can be neglected in the calculation. Additionally, simple water treatment can be done as well such as by constructing artificial aquifer before water entering this reservoir. This report mainly will stress on how to calculate optimal volume of resevoir to be needed to collect water from rainfall on the basis of giving optimal supply of water to fullfill demands. Any calculation for different rates of demand lasser than the optimal one can be elaborated as well whenever necessary to meet this specific purpose, however, as a trade off the volume of reservoir needed becomes bigger and more expensive. (oleh; Bambang Sonarto*, Wawan Herawan*/Peneliti Puslitbang Pengairan)
Perhitungan Volume Tampungan Air Hujan Optimal Melalui Atap Bangunan Guna Mengatasi Kekurangan Air Bersih
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