Temps de lecture :6 minutes
All it takes is a roof, a gutter and a tank to lift the poor out of drudgery. But is it that simple, ask Aisling Irwin and Aditya Ghosh?
Mr Wijesinghe, of Meewellawa village, in the dry northwest of Sri Lanka, used to dread his neighbours calling round. A call, by custom, means serving a cup of tea. His well was dry for increasing portions of the year — and every drop had to be fetched from up to 4km away.
That was before last year’s installation of a system that collects rain from his roof and diverts it into a tank and a pond. Now, Wijesinghe has drinking water. In addition, water percolating down from the pond has recharged his well and also irrigates a lush new garden rich in fruit and vegetables that he sells. His family has time for other activities.
As for a cup of tea — his door is always open.
Wijesinghe’s story is one of thousands repeated across Sri Lanka and in other countries. Lives are lifted from the drudgery of fetching water. Wasted hours are diverted into more productive tasks. And it is all thanks to a simple intervention.
Proponents of rainwater harvesting say it should be massively expanded and may present the poor’s best defence against water scarcity induced by climate change. But the world is also scattered with tales of roof catchment failures — and academics who say its potential for ending water insecurity is oversold.
An ancient pedigree
Catching rainwater is an ancient technology which has risen and fallen in popularity over the centuries. Recently, its favour dwindled as groundwater — a generally high-quality, naturally distributed source that offered economies of scale, became popular.
But, over the past decade, rainwater has made a comeback for those having to dig deeper as their water tables sink; or whose groundwater has been infiltrated by fluoride, arsenic or salt.
In Sri Lanka, the great Indian Ocean tsunami of 2004, which contaminated water in coastal areas with bacteria and sea water, accelerated a growing rainwater harvesting movement, according to Tanuja Ariyananda, director of the Lanka Rain Water Harvesting Forum. At the last count, the 20 million-strong population included 35,000 households with domestic rainwater installations.
Not for everyone
Nature gave Sri Lanka an average annual rainfall of an impressive 1,700 mm, although dry areas can go for up to six months without water.
But Sri Lanka’s success is not necessarily repeatable everywhere, says Terry Thomas, senior lecturer in the school of engineering at the University of Warwick in the United Kingdom, which has been involved in roof water harvesting projects in several countries.
Thomas, who says he is a “modified enthusiast” for the activity, says there are many unsuitable places.
“If there is a six-month dry season it’s pretty uneconomic to do it,” he says. Other routes to water security may be preferable — for example, Middle Eastern nations that are energy-rich but have low rainfall are more suited to desalination.
Uganda, in contrast, has two rainy seasons with only six weeks of dry season — perfect for rain collection. South East Asia and parts of the Amazon jungle are similarly well-endowed, he says.
Roof catchments are also, of course, a solution for the desperate wherever they find themselves — those who live on hill tops where fetching water means back-breaking toil; or where the ground is hard to drill; and those living in areas like north-eastern Brazil where, says Thomas, there are “no rivers, no aquifers and modest rainfall”.
Storage is expensive
Although roof catchment may sound like a cheap option, it needs guttering and piping and — most expensively — storage.
In Sri Lanka each household installation, which includes a 5,000-litre ferro-cement tank, costs US$300, including skilled labour. But it can be done more cheaply, says Brett Martinson, senior lecturer in environmental engineering and sustainable development at the University of Portsmouth in the United Kingdom. By keeping away from the frills that inventors keep adding, and opting for a more modest, 500 to 1,500 litre collecting pot, costs could be cut to around $50.
That can still be too much for the very poor, at whom many of the schemes are targeted. So roof water catchment schemes have usually been subsidised by non-governmental organisations, foreign donors, or national governments. This has led, say critics, to the culture of dependency that is common to failing development projects.
“All the programmes over the years have pulled it off by having subsidised systems,” says Thomas. “No-one will ever shell out for a non-subsidised system — they wait for another to come along.”
And this “anarchic, small-scale, diffuse intervention”, as Martinson calls it, offers little scope for the economies of scale that help drive prices down with centralised water distribution.
Rainwater needs laws
Yet in Sri Lanka, the expense does not seem to have impeded relatively long-term success. Donors and government subsidies have indeed bought kit over the years but crucially, according to Ariyananda, government support means rainwater harvesting is unlikely to die away should donors withdraw.
Sri Lanka launched a national rainwater harvesting policy in 2005, followed by legislation. In urban areas, for example, new buildings above a certain size must harvest rain from their roofs.
Government drive is pivotal to nationwide success in roof catchment schemes, according to Vessela Monta, executive director of the International Rainwater Harvesting Alliance, in Switzerland.
“For me, a success story is when a country elaborates a law on rainwater harvesting — when it comes into a development plan,” says Monta. “This is the most important step.”
Popularity with governments appears to be growing.
“When we started (in 2002), only professionals were aware of the value of rainwater harvesting,” says Monta. “People considered we were doing something marginal, linked more with traditions than with the future. It has been a very intensive period of change.”
Now, interest in rainwater harvesting in general, and roof catchments in particular, has spread, partly because rainwater harvesting systems were included in the list of ‘improved water sources’ specified by the United Nations Millennium Development Goals in 2000. Countries with policies, and even legislation, include India, Kenya and Uganda.
The importance of government support, says Monta, lies partly in the fact that it leads to strong national organisations that can drive harvesting projects, train villagers in their new systems, and organise skilled maintenance back-up. Encouragingly for the rainwater enthusiasts, surveys in Sri Lanka show that 80 per cent of installations are working well, which Ariyananda attributes to this.
Effects of climate change
Yet, for a simple technology, says Martinson, there’s a mighty number of tiny things that can go wrong.
Mosquitoes can breed in lidless tanks; algae will thrive in sunlit water; tanks must be ventilated to achieve the right temperature; Misguided and fastidious tank owners sometimes scrub inside their tanks, clearing out benign bacteria that feed on the dangerous ones — inadvertently raising their risk of disease. At the other end of the system, roofs that are inaccessible for cleaning get dirty.
But these are surmountable problems and most experts seem to think there is an increased role for roof catchment in insulating the poor against the effects of climate change. This is despite the fact that decreased rainfall and longer dry seasons may reduce its effectiveness in many places.
This is because climate change is likely to worsen the other water options too, with decreased groundwater recharge reducing the capacity of wells, and rising sea levels spoiling coastal water sources.
“My gut feeling,” says Martinson “is that climate change won’t help [make roof catchments more effective]. But it won’t help anything else either — it’s whether rainwater harvesting is more or less affected [than other water sources]. “
Ariyananda, however, is convinced about the potential of roof catchments.
“It’s something we should promote as adaptation for climate change,” she says. “They are predicting more rains, with higher intensity, for shorter times — and big problems with water.
“Rainwater harvesting is the only solution”.
Thinking outside the tank
Indeed some experts believe that roof water harvesting could be much more ambitious.
Rajendra Singh, an Indian famous for his regeneration of ancient water harvesting technologies in the dry northeast of Rajasthan region, in India, argues that city buildings should all be collecting water.
Singh is calling for Bangalore, Chennai, Hyderabad, Kolkata, Mumbai New Delhi and Pune, all of which are reeling under severe water shortages, to make it compulsory to harvest rainwater from the roofs of buildings.
“This will have two benefits,” he says. “The water table in the cities will be recharged which, with overexploitation for half a decade, have diminished.
“The other benefit is even more important: that these cities will have to draw less water from the rivers, lakes and other natural sources which are all located in rural areas, forested lands and away from the city.
“This will help the poor, who are often denied the most vital resource of life in order to supply urban areas.”
As an example of potential benefits he cites Bangalore, the information technology hub of the country. It recently developed a master plan for 1279 sq km of its land, predicting that rainwater harvesting could meet a quarter of the city’s water demand.
It is now mandatory in cities such as Chennai and Mumbai for all large, new constructions to install rainwater-harvesting facilities. But existing buildings are exempt.
“There are isolated efforts,” says Singh, “which can no longer make a perceptible difference.
“The situation is precarious and needs attention at all possible levels.”
by Aisling Irwin is SciDev.Net’s news editor. Aditya Ghosh is an environmental journalist based in India.