Rainwater harvesting is any method that gathers, accumulates and stores rainwater. The collection of rainwater is either from natural or man-made surfaces. Rainwater harvesting is being used for productive purposes such as drinking water for people and livestock, irrigation, recharge of aquifers, household activities, construction etc.
In arid environments rainwater harvesting is usually applied to supplement other existing water sources, while in humid regions harvesting may provide enough water for all demands.
In some cases, rainwater may be the only available, or economical, water source.
Two main approaches to harvesting water for agricultural purposes are distinguished:
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Micro-Catchment Water Harvesting (MCWH) which largely deals with gathering surface runoff and transferring it in the water unsaturated (vadoze) root zone of soils; and
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Runoff Farming Water Harvesting (RFWH) where water is routed by diversion systems to a storage system for subsequent application in irrigation or for livestock consumption.
A further approach for water harvesting in settlements is Domestic Rainwater Harvesting (DRWH), which focuses on gathering water from a surface (commonly house roofs), diverting it for safe storage. Corrugated metal sheets have proofed as most effective surface collectors. Household rainfall catchment systems are suitable in areas with an average annual precipitation of more than 200 mm.
Rainwater Harvesting
A rainwater harvesting system consists of the supply (rainfall), the demand (water needed by plants), and a system for collecting water and transporting it to plants. Simple systems distribute rainwater immediately. More complex systems store some or all of the rainwater for later use. Basic considerations in rainwater harvesting systems are:
Rainfall. “Run-off” is the rainwater that flows off a surface. If the surface is impermeable (pavement, concrete, tin roofs), run-off occurs immediately. If the surface is permeable, run-off will not occur until the surface is saturated. Run-off can be harvested (captured) and used immediately to water plants or stored for later use.
Water collection and distribution system. Rainwater collection and distribution systems can be incorporated into almost any existing site, although it is easier to incorporate them into new construction.
Epako community garden irrigated with rainwater collected.
Source: Water Charity 2009
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Namibia
A number of NGOs are involved in rainwater harvesting for rural communities. UNICEF supported construction of water tanks in schools in the Ovambo Region on the northern border with Angola, RISE Namibia has implemented a pilot domestic rainwater harvesting project in the Erongo region in the northwest, and IBIS is supporting rainwater harvesting initiatives in the north as part of an ecological housing project.
Various initiatives have been planned and commenced for rainwater collection to augment irrigation of community gardens. One such example is the Epako Rainwater Harvesting project near Gobabis, in the Omaheke Region of Eastern Namibia.The project is funded by the local NGO Early Intervention Programme and aims to ensure that healty food is available for the youth, promote their skill development and responsibility, and foster self-esteem.
A further example is the UNDP and Omalundu Iimuna Kommitiye Elungameno project funded by GEF (Global Environmental Fund) that provides the Onkani community (Omusati Region) with practical tools for adaptation and increasing community awareness about climate change risks. Among other measures the project supports the implementation of small-scale rainwater harvesting and storage methods to improve water conservation and usage while adapting to more erratic and heavy rains predicted. The project is implemented by the Okani community with support from Ministry of Agriculture, Water and Forestry, the Desert Research Foundation of Namibia, and the Namibia National Farmers Union.
In the framework of the CuveWaters project pilot plants for rainwater collection have been installed in participation with the villagers of Epyeshona (Oshana Region) in 2009 and 2010. The plant consists of various surface and subsurface reservoirs with capacities between 30 and 120 m³. The water collected is used for irrigation purposes as well as for laundry washing and livestock watering. Additional information about this pilot project can be obtained in the Document Centre.
Additional information on this subject is included in the Climate and Weather chapter.
Surface reservoir for rainwater collection in Epyshona, Namibia.
Source: CuveWaters 2010
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