Harnessing the rain

Water harvesting really works and governments in sub-Saharan Africa have a key role to play in promoting it, writes Maimbo Malesu. Chiefly, they can provide financial incentives and grants for rural and urban projects.

The following extract, published with permission, is from the Worldwatch Institute’s State of the World 2011: Innovations That Nourish the Planet. The full report is available from Earthscan (non-US readers) and Worldwatch (US readers).


There is an overdependence on rain-fed agriculture in sub-Saharan Africa and not enough ways to deal with the effects of dry spells and droughts. As a result, grain yields are below one tonne per hectare in most of the region. This has mistakenly been blamed on physical water scarcity. But it is not physical as much as it is economic. There is simply a lack of investments to both capture and boost water storage.

Most sub-Saharan African countries are currently using at most 5% of their rainwater potential. By recognising and incorporating the greenwater — the water ignored in hydrological planning — it may be possible to improve the food insecurity situation while also protecting the environment.

To help alleviate hunger and poverty, the Swedish International Development Cooperation Agency (SIDA), through its Regional Soil Conservation Unit, helped establish the Southern and Eastern Africa Rainwater Network (SearNet) in 1998. SearNet consists of 12 national rainwater associations that work together to publicise rainwater harvesting information and innovations throughout the region. The network is hosted by the World Agroforestry Centre in Nairobi.

In collaboration with Rwanda’s ministry of agriculture and animal resources, the World Agroforestry Centre pioneered a method for upscaling trapezoidal-shaped ponds with off-stream runoff water conveyance mechanisms that facilitate the supply of water for irrigation and livestock development. The ponds can hold 120 cubic metres of water and are lined with a 0.8-millimeter plastic sheet. Inexpensive materials, including rope, a washer pump and a siphon or easy-to-use treadle pump are used to bring the water up from the pond.

As the pond costs around US$800, farmers would need a subsidy, a cost-sharing facility, or microfinancing to afford one. But the payoffs can be huge. Cost-benefit studies indicate that, with good management, farmers recover their investment costs in just two or three years.

With access to more water, farmers are encouraged to plant vegetables such as kale, tomatoes and onions as well as fruit trees, including mangoes and pawpaws [papayas], to boost production and improve nutrition. This innovation has spread across 10 districts in Rwanda: more than 400 ponds have been constructed and 800 more are in the pipeline.

Rural women spend at least three to four hours a day collecting water from distant and often contaminated water sources for use in cooking. This is especially burdensome for girls who are in school; they have to wake up early in the morning, haul water and then rush off to class.

In the Kajiado District of Kenya, the UN Environment Programme (UNEP) and the World Agroforestry Centre have worked with Maasai women to build roof catchment ferro-cement tanks to provide domestic water for their households. Members of women’s groups were encouraged to donate some of their own money so they could get matching funds from UNEP and the centre. The women also provided local materials such as water, sand and stones as well as labour for construction of the tanks.

After initial training, 86 tanks were constructed. In addition, the women were encouraged to plant 100 trees for each tank built. The project is being upscaled on a rotational basis, with a target of each woman eventually having her own tank. Rotary International of Canada then adopted this community, and more than 200 tanks have been constructed using the same model. This has improved health, and the women have more time for other fund-raising activities.

Farmers do not need expensive gadgets to find groundwater to help irrigate their crops. Green twigs, copper wires and plumb bobs can be used to locate and determine the width and status of underground water bodies. Green twigs from Croton megalocarpus or C. microstachys tree species found in semi-arid lands have been known to perform better than those from other tree species. The copper wire is used to determine the width of an underground water body, while the plumb helps estimate the depth.

All in all, these tools have been used to map underground water bodies. A comparison with terrameters, the devices used by civil engineers in groundwater prospecting, has confirmed that these other tools are not only cheap (or free, for the twigs), but also accurate.

In the western and Rift Valley regions of Kenya, water can be the entry point to rural development. Harnessing rain through water harvesting and conservation agriculture methods such as no-till farming and cover crops provides the basis for productive ventures that are crucial in helping to increase food self-sufficiency and improve rural economies. For annual crops, changes in yield are immediate. For perennial crops, it takes a few years before the impacts are realised. But with good agricultural husbandry, it is possible to realise positive returns when the availability of water or moisture is integrated with soil fertility management.

Water harvesting is more than just a matter of constructing ponds, dams, wells or tanks, of course. It is a slow process of creating, of organising communities to develop, maintain and manage water-harvesting activities, of involving communities closely in every aspect of the project, and of setting up systems for using and sharing water sustainably and equitably. This is also precisely the reason why it has to be a matter of community involvement and participation.

It is crucial, therefore, to create awareness and confidence among farmers and communities that water harvesting really works. The government should be a facilitator rather than an implementer. It has an important role to play in catalysing the widespread practice of water harvesting. And the government could get scientific organisations to develop better designs of the systems. But the most important role for government is to provide financial incentives and grants for water harvesting in rural and urban areas.

Maimbo Malesu is the World Agroforestry Centre’s water-management programme coordinator for eastern Africa.

This extract, published with permission, is from the Worldwatch Institute’s
State of the World 2011: Innovations That Nourish the Planet. The full report is available from Earthscan (non-US readers) and Worldwatch (US readers). State of the World 2011: Innovations That Nourish the Planet © Copyright 2011, Worldwatch Institute

Homepage photo by the United Nations/Evan Schneider shows Tanzanians beside a water storage tank provided by the UNICEF water harvesting project.