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[[Image:Rainwater_harvesting_icon.png|right|100px|]]

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.

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.

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.

====Drought====

Making cement in regards to drought: [[Concrete production and drought]].

[[Image:rooftop catchment.jpg|thumb|right|200px|Rooftop catchment. Drawing: WHO.]]

The flow of water can be intercepted in different ways. Different catchment types are used, such as roof catchment, paved surface catchment, surface catchment and riverbed catchment. The cheapest storage of all is to use the ground as storage area, a technique called groundwater recharge. It is accomplished by letting rainwater infiltrate in the ground. The recharge will locally lead to a higher water table, from which water can be pumped up when needed. Whether the infiltrated water raises the water table in a local area or is spread across a wider area depends on soil conditions.

====Keeping the water clean====

====The EMAS filtration system ====

The EMAS system for rainfall collection uses various EMAS technologies as well as simple tools to convert rainwater into usable drinking water. If roof rainwater is being used, it is collected through a regular gutter. To filter the water, at the bottom of the gutter, a pitcher or ferrocement tank is placed, with an outlet pipe. A synthetic cloth bag is attached to the rim of the pitcher using an iron ring or wire, which fits around the edge. The bag should be cleaned every 3 months.

====Maintenance====

* financial investment needed is not affordable - households or communities cannot afford to construct a suitable tank and adequate roofing.

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>

* 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.

* A low-cost option is the [[brick cement tank]], used in for example Nicaragua and Ghana.

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====Manuals====

* Booklet [http://www.washdoc.info/docsearch/title/169828 Smart Water Harvesting Solutions]

====Videos====

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====External links====

* [http://www.rainfoundation.org Rainwater Harvesting Implementation Network (RAIN)]

* [http://www.rainwaterharvesting.org Indian website on rainwater harvesting ]

* [http://en.wikipedia.org/wiki/Rainwater_harvesting Wikipedia article on rainwater harvesting]

* [http://www.eng.warwick.ac.uk/dtu/rwh Rainwater Harvesting info on the DTU unit of University of Warwick]

* [[Solution_of_the_week_5|Akvo solution of the week 5]]

<references/>

* 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.