“Let not a drop of water that falls from the sky flow into the sea….”
These were the words of Parakramabahu, a 13th century Sri Lankan monarch who constructed the Sea of Parakrama,a massive rainwater harvesting reservoir, which to this day irrigates vast stretches of paddy fields in the Gal Oya district of the country.
Rainwater harvesting has gained in popularity throughout the island in the past decades. It is a technique of conservation in which rainwater is harvested form roof and ground catchments, safely stored in special tanks and used when the rains fail. Sri Lankan archeologists have discovered a whole network of storage reservoirs, pools, artificial streams and fountains in the north and central regions of the country proving that rainwater has been an integral part of the irrigation system of the country.
Annual rainfall
Sri Lanka has an annual rainfall volume of about 5,900 cubic metres from which the annual discharge into the sea is about 1,400 cubic metres. Most parts of the country are blessed with rain from two seasonal winds that flow across the country. These, called ‘monsoons’, are active in the north east from May to September and in the South West from November to April. However, due to a number of factors such as vagaries of rain, improper land management practices as unrestrained filling of low lands and restriction of natural drainage paths and due to insufficient storage mechanisms, a substantial amount of water flows into the sea.
Pioneering forum
The importance of conserving rainwater rather than letting it flow into drains and into low lying areas has been a crucial concern. The Lanka Rainwater Harvesting Form ( LRWHF) has been engaged in pioneering work in conserving rainwater in the past couple of decades and their efforts resulted in a national policy on rainwater harvesting introduced last year (2009).
“Sri Lanka is the only country in the world to have a national policy on rainwater harvesting.” Says Dinesh Gunwardenea, Minister of Urban Development”. Tanuja Ariyananda, Director of LRWHF says that the objectives of the policy are in keeping with the increasing costs of pipe borne water supply, drainage, flood control and soil conservation.
Primary school Aukanna, Anuradapura
Minister: Make rainwater harvesting mandatory
“The plan is to make rainwater harvesting mandatory, introducing it first in stages in all urban areas within a prescribed period and covering certain categories of building and development projects for a beginning,” explains Ariyananda.
She adds, “the policy aims to upgrade the status of rainwater from a supplementary – which it is at present – to an optional source in all rural based water supply projects.”
Benefits and hurdles
Sri Lanka sees several benefits of rainwater harvesting. Apart from minimizing the use of potable water for secondary purposes, it prevents depletion of ground water, reduces water stress during droughts and lowers salinity intrusion.
A major hurdle that has to be overcome in popularizing rainwater for domestic use is the mindset of the people who believe that rainwater is impure and not suitable for drinking. The LRWHF has had intensive training for masons in building tanks for storage and given demonstrations in households on the operation and maintenance of rainwater harvesting systems. LRWHF has also built links with local agencies and international rainwater harvesting ventures to exchange information and to communicate through awareness programmes..
“There is one snag, however,” says Ariyananda. “rainwater lacks minerals and those who depend totally on rainwater for drinking must make sure that they add the minerals to their food.”
Vijita Fernando, Sri Lanka, e-mail: vijita@sltnet.lk
In the UK we have a British Standard for rainwater harvesting, the BS8515 2009 which limits the size of rainwater harvesting tanks to avoid the risks involved with storing stagnant water, e.g. Legionnaires Disease.
We are limited to a tank which is the smaller of either 5% of the annual useage or 5% of the volume of water that falls on the roof/year.