5th International Conference on Rain Water Cistern Systems
"Rainwater Catchment for Future Generations"
Keelung, Taiwan, R.O.C. - August 1991

Section 11: Technical Short Papers

Page 737

Rain -Water Harvesting - The Constraints

H.C. De Silva
Irrigation Department, Sri Lanka

Abstract

Water resource exploitation for human; needs has grown: by, leaps and bounds in the last two decades. Nearly all the suitable sites for storage dams and river diversions have been utilized and ground water 'extracted regardless of consequences as in Bangkok

Water for all by the year 2000 still remains an ideal, Rivers that were once perennial now become, raging torrents that convey their runoffs in the form of flash flooding.. As forests are reduced by deforestation and catchments urbanised the need to harvest rain before it reaches the dry streams beds or fall into polluted rivers becomes of paramount importance.

Runoff areas: in catchments continue to diminish and are replaced by concrete paving or bitumen. covered roads or asbestos or tiled roofs. Rainfall runoff from such artificial catchments can be collected in cisterns. above ground or in tanks below Preserving the rain close to where it fell avoids contamination that occurs with surface runoff : Percolation and. evaporation loss °is reduced: But rainfall in urban areas has its drawbacks when atmospheric pollution sulphur dioxide and carbon dioxide from vehicular traffic; coal fired power stations or industrial flue gases can convert the composition of rain to acid rain is very real.

Collection of rain in cisterns also could attract growth 'of organisms and larvae that could promote diseases like malaria, filaria, dengue and Japanese encephalitis, if such water is consumed without boiling. Water -stored in. underground- cistern could be contaminated by leakage from septic tanks. in the proximity adding nitrates and phosphorous Cisterns take up space in high value urban areas.

Population growth the world over has mushroomed to such extents that efforts made by countries to supply their basic requirements of water for drinking;. for 'irrigation and for power production can hardly copy with.

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