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Monday, 12 December 2011






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Harvesting rainwater means harnessing life

Regulations will be introduced to make rainwater harvesting for daily use compulsory for all government institutions, Water Supply and Drainage Minister Dinesh Gunawardane said in Parliament recently. The minister said he introduced this concept when he was the Urban Development Minister. He said rainwater harvesting is done successfully in countries such as India and Nepal.

Water professionals in Sri Lanka are becoming increasingly worried about the country's impending water scarcity. They suggest that the population growth, pollution and climate change are likely to produce a drastic decline in the amount of water available per person in many parts of the country.

Water conservation, therefore, has become the need of the day. And it is here that the concept of Domestic Roof Water Harvesting (DRWH) comes into place. DRWH provides an additional source from which to meet local water needs. In recent years, DRWH systems have become cheaper and more predictable in performance. There is a better understanding of the way to mix DRWH with other water supply options, in which DRWH is usually used to provide full coverage in the wet season and partial coverage during the dry season as well as providing short-term security against the failure of other sources. Interest in DRWH technology is reflected in the water policies of many developing countries, where it is now cited as a possible source of household water.

Schematic diagram of domestic rainwater harvesting system

Rainwater systems deliver water directly to the household, relieving the burden of water-carrying, particularly for women and children. Collecting the water that falls onto household roofs provides an attractive method of conserving water delivered directly to the home. 'Water without walking' relieves families of much of the burden of water-carrying.


There has been much recent activity concerning domestic roof water harvesting in countries as far apart as Kenya, China, Brazil and Germany. Many countries now have Rainwater (Harvesting) Associations. Lanka Rain Water Harvesting forum (LRWHF), a similar organization, was launched in Sri Lanka in 1996 with the vision of 'leading the nation in rainwater harvesting technology, construction and utilization to sustain water needs'. The organization was instrumental in spreading the concept and technology to many parts of the country. It is said that there are more than 30,000 domestic rainwater systems in the country.

Domestic rainwater harvesting has been revived in Sri Lanka in 1995. Ten years later, in 2005 the government, realizing the importance of rainwater harvesting as a solution to overcome the water scarcity in the country, passed a national policy on rainwater harvesting.

The policy objective is aimed at encouraging communities to control water near its source by harvesting rainwater. The policy was followed by necessary legislation which was gazetted on April 17, 2009, to amend the Urban Development Authority By-Laws on drainage, which makes rainwater harvesting mandatory in certain categories of new buildings in areas under municipal and urban council jurisdiction.

Why rainwater harvesting?

Like in many regions of the world, in Sri Lanka, too, clean drinking water is not always available and this is only possible with tremendous investment costs and expenditure. Rainwater is a free source and relatively clean and with proper treatment it can be even used as a potable water source. In Sri Lanka, rainfall is the primary source of water. The mean annual rainfall is around 1,800 mm with some areas receiving only about 900 mm. The total amount of water received in the form of rain is around 100 billion cubic metres per year. It is estimated that out of the total water received, over 50 percent escapes to the sea as run-off. It means, around 50 billion cubic metres of water finally ends up in rivers, reservoirs and sea.

Rainwater harvesting saves high-quality drinking water sources and relieves the pressure on sewers and the environment by mitigating floods, soil erosions and replenishing groundwater levels. In addition, rainwater harvesting reduces the potable water consumption and consequently, the volume of generated wastewater.

There are numerous positive benefits for harvesting rainwater. The technology is low cost, highly decentralized empowering individuals and communities to manage their water. It has been used to improve access to water and sanitation at the local level. In agriculture rainwater harvesting has demonstrated the potential of doubling food production by 100 percent compared to the 10 percent increase from irrigation.

The biggest challenge with using rainwater harvesting is that in many cases water management is based on renewable water, which is surface and groundwater with little consideration of rainwater. Rainwater is taken as a 'free for all' resource and the last few years have seen an increase in its use. This has resulted in over abstracting, drastically reducing water downstream users including ecosystems. For the sustainable use of water resources, it is critical that rainwater harvesting is included as a water sources as is the case for ground wand surface water.


There is an immediate need to find innovative opportunities enabling development and human wellbeing without undermining ecosystem services. Among such opportunities one can ask: What potential can rainwater harvesting offer to enable increased human well-being whilst protecting our environment? What role can small-scale decentralized rainfall harvesting and storage play in integrated water resource management? And in which specific contexts may rainwater harvesting create synergies between good ecosystems management and human well-being?

Today, more people live in urban areas than in rural areas globally. Cities can be considered as 'artificial ecosystems', where controlled flows of water and energy provide a habitat for the urban population.

Accordingly, the principles of ecosystem management also apply to sustainable urban water management. Rainwater harvesting has increasingly been promoted and implemented in urban areas for a variety of reasons.

The effect of multiple rainwater harvesting interventions on ecosystem services in urban areas are two-fold. Firstly, it can reduce pressures of demand on surrounding surface and groundwater resources. Secondly, the rainwater harvesting interventions can reduce storm flow, decreasing incidence of flooding and short peak flows.


In Australia, withdrawals of water supply to the urban areas have been diminishing due to recurrent droughts. This has spurred private, commercial and public house owners to invest in rainwater harvesting for household consumption. The increased use of rainwater harvesting provides additional water supply and reduce pressures of demand on surrounding surface and groundwater resources.

In most of Indian states, all commercial and institutional buildings, tourist and industrial complexes, hotels etc, existing or coming up and having a plinth area of more than specified square metres should have rainwater storage facilities commensurate with the size of roof area. Toilet flush systems will have to be connected with the rainwater storage tank.

In parts of Japan and South Korea, rainwater harvesting with storage has been implemented also as a way to reduce vulnerability in emergencies, such as earth quakes or severe flooding which can disrupt public water supply.


To promote rainwater harvesting and utilization as an environmentally sound approach for sustainable water management, a network should be established involving government administrators, citizens, architects, plumbers and representatives of equipment manufacturers.

It is essential to encourage regional exchanges amongst public servants, citizens and industry representatives involved in rainwater storage, seepage and use, as well as the conservation and reclamation of water. The relevant implementation policies should then be established to make rainwater utilization and other measures a part of the social system.

* Let us accept rainfall as an important manageable resource in water management policies, strategies and plans. Then rainwater harvesting interventions are included as a potential option in land and water resource management for human well-being and ecosystems productivity.

* Let us realize that rainwater harvesting is not a 'silver bullet', but it can be efficient as a complementary and viable alternative to large-scale water withdrawals, and reduce negative impacts on ecosystems services, not least in emerging water-stressed basin

* Let us treat rainwater harvesting as a local intervention with primarily local benefits on ecosystems and human livelihoods. Stakeholder consultation and public participation are, therefore, key to negotiate positive and negative trade-offs potentially emerging, comparing rainwater harvesting interventions with alternative water management interventions.

* Let us agree that the access and right to land can be a first step to rainwater harvesting interventions. Special measures should be in place so rainwater harvesting interventions also benefit land-poor and landless in a community.

*Let us establish enabling policies and cost -sharing strategies, (including subsides) to be provided together with technical know-how and capacity building.


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