Preparing for water scarcity

Many scientists thought that global warming would make the rainfall in humid tropical areas such as Sri Lanka even greater. Indeed, research published in the magazine ‘Science’ in last April shows that, based on changes to the salinity levels of the oceans in the period 1950-2000, the world’s wet areas have got wetter.

However, Sri Lanka is apparently bucking the trend. Studies done by researchers at the University of Colombo have indicated that the rainfall pattern has changed in the past 60 years: there has been progressively less rain in the wetter areas of the island, while there has been an increased intensity of precipitation in shorter rainy spells, with longer dry spells.

This year’s weather pattern certainly appears to be following this trend, with some rainfall in Colombo but not in the vital upcountry catchments. As global warming heats up, it is likely that the new configuration of precipitation will deepen in effect, causing drought in the catchment areas and floods elsewhere.

The problem is exacerbated by the depletion of forest cover, especially in the vital upcountry sources of the major rivers. The loss of forest cover decreases the ability of the soil to retain water and hence rainwater pours downhill much faster, instead of running slowly to enable a constant flow to the rivers. This, together with the change in intensity of rainfall has led to increased occurrences of floods and droughts.

Better conservation

Our forward planning for the rest of the century will have to take this unpalatable fact into account. Our reliance hitherto on abundant rainfall and gushing streams and rivers will have to be adjusted to a more meagre supply of water. This has enormous ramifications, not merely for supplies of potable water, but for other uses - in agriculture, in hydroelectric power generation, in industry and in homes. There are three principles which must be inculcated into the national psyche if we are to be able to face shortages of water in the future: more storage, better conservation and greater re-use. The ancient hydraulic engineers well understood these principles, as they built irrigation tanks in cascades downstream of one another. Indeed, ancient Sri Lankans were imbued with far greater appreciation of the value of water than we are today. This is well illustrated by the passage in the Culawamsa in which King Dhatusena raises the water of the Kalaweva tank in his hands and declares it to be his treasure, to the chagrin of his patricidal son Kasyapa.

Ancient irrigation tanks

The water fetish of antiquity is further exemplified by the lotus ponds of Anuradhapura and the water gardens of Sigiri. Water was thus synonymous with pleasure and was at the same time sacred, signifying purity and goodness. Our culture is permeated with the same principles, but these have become ritualistic in the modern era of the abundance of water. We must re-instil in the populace the practical aspects of our ancient hydraulic heritage.

The best way to improve storage is to allow nature to do its work and restore forest cover. The ancients, unlike their modern descendants, hesitated to cut down trees - Dutugemunu is reputed to have named the Ruwanweliseya Dagoba for the deity of the tree that he was forced to cut down to build it.

It is necessary once more to inspire in our people the old love for verdant nature: there should once more be many trees in each home garden, allowing greater preservation of the water table in urban areas as well as rural. Storage capacity can be improved by renovating the hundreds of ancient irrigation tanks which dot the landscape. And each household should be made harvest and store rainwater. Water can be conserved by better irrigation techniques - such as drip irrigation for non-paddy crops. Where tube wells are used, it is essential that the rate of extraction is not greater than the ability of the ground-water source to recharge itself.

The reduction of electricity use is a means to conserve the water in hydro-electric reservoirs, particularly in the dual-use (irrigation and power) Mahaweli river system.

Shops, offices and houses can benefit by the replacement of existing equipment by less water-extravagant apparatus. The dual-flush cistern, with a choice of two discharge volumes, and the knee-operated wash-basin tap (the latter especially in canteens and communal toilets) are obvious examples of what is required.

Re-use of water

However, the technology differential need not be all that great: the use of a mop rather than an ‘ilapata’ to wash floors, the use of a shower instead of a bathing bucket, and so on. The re-use of water can best be achieved by re-using wash-water - technically called ‘grey water’. The more modern hotels already use grey water for gardening purposes. It can also be used (in conjunction with harvested rainwater) to flush toilets, to wash floors and motor vehicles.

Indeed, much precious potable treated municipal water is used for washing purposes for which such high standards of hygiene are not required. Ideally, municipal water should consist of two separate pipeline systems, one for potable-level treated water and the other for grey water and harvested rainwater, for two levels of use.

Water from sewage can also be re-used, suitably purified. The British engineers at the Ratmalana railway workshops reputedly drank the purified water from the sewage treatment plant there to prove how clean it was, with no adverse effects. In order for such measures to be implemented and to be effective, there must be a groundswell of opinion in their favour. This can only be achieved by educating the public about the immediacy of the dire water crisis which faces us.