Rainwater harvesting refers to structures like homes or schools, which catch rainwater and store it in underground or above-ground tanks for later use. One way to collect water is rooftop rainwater harvesting, where any suitable roof surface — tiles, metal sheets, plastics, but not grass or palm leaf — can be used to intercept the flow of rainwater in combination with gutters and downpipes (made from wood, bamboo, galvanized iron, or PVC) to provide a household with high-quality drinking water. A rooftop rainwater harvesting system might be a 500 cubic meter underground storage tank, serving a whole community, or it might be just a bucket, standing underneath a roof without a gutter. Rainwater harvesting systems have been used since antiquity, and examples abound in all the great civilizations throughout history.
===Introduction===
In many cases, groundwater or surface water may be unavailable for drinking water. The groundwater level may be too deep, groundwater may be contaminated with minerals and chemicals such as arsenic or salt, surface water may be contaminated with faeces or chemicals. In these cases, rainwater harvesting can be an effective and low-cost solution.
Another option is to use water from different sources. Water that is salty or has arsenic might still be good enough for washing and sanitary purposes. High-quality rainwater, caught and stored in a tank can then be used for drinking and cooking.
===Suitable conditions===
Rainwater harvesting requires at least an annual rainfall of 100-200 mm. Many places in Latin America have rainfalls of about 500 millimeters per year.
===Resilience to changes in the environment===
====Drought====
Making cement in regards to drought: [[Concrete production and drought]].
===Construction, operations & maintenance===
[[Image:rooftop catchment.jpg|thumb|right|200px|Rooftop catchment. Drawing: WHO.]]
* financial investment needed is not affordable - households or communities cannot afford to construct a suitable tank and adequate roofing.
===Costs===
Comparison of costs
* [[Brick cement tank]] of 6 m3: 3 bags of cement, 300 bricks, 3 kg of wire US$ 40
In Southern Africa, US$ 320 for a system with 11 m of galvanized iron gutter; a 1.3 m3 galvanized iron tank; downpiping; tap and filters; cost does not include transportation. Where roofs are not suitable for water harvesting, the cost of roof improvement and gutters will have to be added to the cost of a tank. Such costs varied from US$ 4 per m2 (Kenya, subsidized) to US$ 12 per m2. <ref name="WHO 1">Brikke, François, and Bredero, Maarten. ''[http://www.washdoc.info/docsearch/title/117705 Linking technology choice with operation and maintenance in the context of community water supply and sanitation: A reference document for planners and project staff]''. World Health Organization and IRC Water and Sanitation Centre. Geneva, Switzerland 2003.</ref>
===Field experiences===
* Rainwater harvesting is a technology which is extremely flexible and adaptable to a wide variety of settings, it is used in the richest and poorest societies on the planet, and in the wettest and driest regions of the world.
* In Ocara, Brazil, rainwater tanks have been constructed of concrete blocks.
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===Manuals, videos, and links===
====Manuals====
* [[Solution_of_the_week_5|Akvo solution of the week 5]]
===References===
<references/>
===Acknowledgements===
* Brikke, François, and Bredero, Maarten. [http://www.washdoc.info/docsearch/title/117705 Linking technology choice with operation and maintenance in the context of community water supply and sanitation: A reference document for planners and project staff] or ([http://www.who.int/water_sanitation_health/hygiene/om/wsh9241562153/en/ alternative link]). World Health Organization and IRC Water and Sanitation Centre. Geneva, Switzerland 2003.
* CARE Nederland, Desk Study [[Resilient WASH systems in drought-prone areas]]. October 2010.