[[Image:Rainwater_harvesting_icon.png{{Language-box|english_link=Water Portal / Rainwater Harvesting / Rooftop rainwater harvesting | french_link=Collecte des eaux de pluie des toits |right]]__NOTOC__[[Image:akkerman.jpgspanish_link=Captación de Agua de Lluvia / Captación de agua de lluvia en techos |thumbhindi_link=वाटर पोर्टल / वर्षाजल संचयन / छत वर्षाजल संचयन |rightmalayalam_link=മേല്ക്കൂരയില് നിന്നും മഴവെള്ള സംഭരണം|300pxtamil_link=coming soon |A women using her water storage tank in Guinnee-Bissau. Photo: Paul Akkerman]]korean_link=지붕 빗물 수집 | chinese_link=屋顶雨水收集 | indonesian_link=Pemanenan air hujan dengan teknik atap bangunan |japanese_link=屋上雨水貯留}}
Rainwater harvesting refers to structures like homes or schools, which catch rainwater and store it in underground or above-ground tanks for later use. 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 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[[Image:Rainwater_harvesting_icon. png|right|100px|]]
[[Image:rooftop rainwater capture.jpg|thumb|right|200px|A rainwater capture system from a small household. Photo: [http://www.jalvardhini.org/storage-01.php Jalvardhini Pratishthan.]]]
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.
It is suitable even when the roof is small. For example a 5 x 6 meters (that is to say 30 square meters) house, with 500 mm annual precipitation, receives a rainfall of 15.000 liters on its roof; this is a sufficient amount for a family formed by 5 members.
{{procontable | pro=
- Possible in almost any climate <br>
- Rainwater generally meets drinking water quality standards, if system is well-designed and maintained <br>
| con=
- Storage is needed to bridge dry periods<br>
}}
{| border="1" cellpadding="5" cellspacing="0" align="center"
|-
! width="50%" style="background:#efefef;" | Advantages
! style="background:#f0f8ff;" | Disadvantages
|-
| valign="top" | - Possible in almost any climate <br>
- Rainwater generally meets drinking water quality standards, if system is well-designed and maintained
| valign="top" | - Storage is needed to bridge dry periods <br>
|}
===Resilience to changes in the environment===
====Drought====
'''Effects of drought:''' Water storage used up. <br>
'''Underlying causes of effects:''' Lack of rainfall; Leaking linings due to bad construction; Storage not sufficient for demand – tanks are too expensive for volumes of water to outlast extended dry periods. <br>
'''To increase resiliency of WASH system:''' Promote smaller tank structures so they are more manageable to construct and cover, while being more affordable to families; Reduce seepage due to poor construction & siting; Follow proper concreting guidelines (see drought effects on cement, below); Make tanks from cheaper lower quality materials and repair more often; Design the outlet of the tank so that there is no dead storage; Ensure the catchment itself is efficient (e.g. gutters); Improve access to micro-finance; Support the capacity of the government or private sector to be able to provide (for payment) a tankering scheme.
====Drought effects on cement tanks====
'''Effects of drought''': Badly made concrete and cracked linings (e.g. in tanks, dams, waterways, wells, and other structures). <br>
'''Underlying causes of effects''': Less water used for curing; Impure water used for mixing. <br>
'''To increase resiliency of WASH system''': Ensure adequate mixing, ratios, purity of ingredients; Minimize water content in mixture; Ensure adequate curing.
More information on managing drought: [[Resilient WASH systems in drought-prone areas]].<br>Making cement in regards to drought: [[Concrete production and drought]]. ===Construction, operation operations & maintenance ===[[Image:rooftop catchment.jpg|thumb|right|200px|Rooftop catchment. Drawing: WHO.]]
====Catchment & storage tanks====
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.
If using storage tanks, structures made with ferrocement or brick-cement are the best and cheapest options, and they can be made locally. When a water tank is below ground, it is called a cistern. Among the different storage types are the [[underground tank]], [[ferro-cement Classical ferrocement tank | ferrocement tank]], [[plastic-lined tank]], etc. The size of the tank is a compromise between cost, the volume of water used, the length of the dry season, etc. It is advisable to first construct a small tank before attempting a large one. Storage tanks can additionally be filled up using pumps. Several pump systems can be used to lift the water from underground tanks, for example with a [[rope pump]] or with a [[deep well pump]], which can elevate water up to a height of 30 m.
====Keeping the water clean====
A foul-flush device or detachable down-pipe can be fitted that allows the first 20 litres of runoff from a storm to be diverted from the storage tanks. This is because runoff is contaminated with dust, leaves, insects and bird droppings. To prevent the use of dirty water, the runoff is then led through a small filter of gravel, sand and charcoal before entering the storage tank, or a filter is placed between the catchment structure and the storage tank. Where there is no foul-flush device, the user or caretaker has to divert away the first 20 litres at the start of every rainstorm.
====The EMAS filtration system====[[Image:Filterrainwater capture2.jpg|thumb|right|150px200px|Filtering the water coming from the gutter]]The EMAS system for rainfall collection uses various EMAS technologies as well as simple tools Two houses are connected to convert a rainwater into usable drinking water. If roof rainwater is being usedcapture unit, it is collected through then a regular gutter. To filter spout provided from 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 monthsPhoto: [http://ispafrica. org Insieme Si Puo' in Africa]]]
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. As water begins to collect, to avoid too much garbage collecting here, first some amount of water is deflected, along with most of the garbage. Hereafter, water can be directly sent to an [[EMAS Cistern cistern]]. It is advisable for multiple cisterns to be available for storage, depending on the size of the roof. Connect one cistern at a time to the outlet pipe. From here water can be pumped and distributed using a regular EMAS pump. The pump can also be connected to faucets and tanks around the house.
====Maintenance====
The system should be also checked and cleaned after every dry period of more than one month. The outsides of metal tanks may need to be painted about once a year. Leaks have to be repaired throughout the year, especially from leaking tanks and taps, as they present health risks. Chlorination of the water may be necessary. Removal of debris and overhanging vegetation from gutters and the roof is important to prevent the gutter being clogged. Tank maintenance consists of physical inspection and repairing cracks with cement. Several studies have shown that water from well maintained and covered rooftop tanks generally meets drinking water quality standards if maintained rightfully. Basic water quality testing is recommended during the first year, with further testing when water quality is in doubt. A low cost water test is the ‘HACH’ test, about US$1 per test. If contamination is suspected or when water quality needs to be guaranteed, the water can be treated in several ways.
Several studies ====Shared roofs====Operation and maintenance (O&M) of shared roofs have shown that more challenges. Rooftop-harvesting systems at schools, for instance, may lose water from well-maintained taps left dripping. Padlocks are often needed to ensure careful control over the water supply. Ideally, one person should be responsible for overseeing the regular cleaning and occasional repair of the system, control of water use, etc. One option is to sell the water, which ensures income for O&M and for organizing water use. Where households have installed a communal system (e.g. where several roofs are connected to one tank), the users may want to establish a water committee to manage O&M activities. The activities may include collecting fees, and controlling the caretaker’s work and the water used by each family. External agents can play a role in the following O&M areas:<br>— monitoring the condition of the system and covered rooftop tanks generally meets drinking the water quality standards if maintained rightfuly; <br>— providing access to credit facilities for buying or replacing a system; <br>— training users/caretakers for management and O&M; <br>— training local craftsmen to carry out larger repairs.<br>
====Manufacture====It is advisable to first construct a small tank before attempting a large one[[File:OandM.A concrete lid protects the tank from pollution. Small fishes can be kept in the tank to keep it free from insectsjpg|thumb|none|500px| Chart: WHO.<ref name="WHO 1"/>]]
==Cost==Comparison of costsPotential problems====* [[Brick cement tank]] of 6 m3: 3 bags corrosion of cementmetal roofs, 300 bricksgutters, 3 kg of wire US$ 40etc.; * the foul-flush diverter fails because maintenance was neglected; * taps leak at the reservoir and there are problems with the handpumps; [[Brick cement tank]] of 1 m3: 1 bag * contamination of cementuncovered tanks, 100 bricksespecially where water is abstracted with a rope and bucket; * unprotected tanks may provide a breeding place for mosquitoes, 1 kg which may increase the danger of wire US$ 20vector-borne disease; * [[Plasticsystem may not fulfill drinking-lined tank]] water needs, during certain periods of 5 m3: US$ 50 the year, making it necessary to develop other sources or to go back to traditional sources temporarily; * Subfinancial investment needed is not affordable -surface ferro-cement households or communities cannot afford to construct a suitable tank of 60 m3: US$ 1,900and adequate roofing.
The bigger the volume ===Costs===Comparison of the storage costs * [[Brick cement tank]] of 6 m3: 3 bags of cement, 300 bricks, the lower the material demand (and thus costs) for construction per 3 kg of wire US$ 40 * [[Brick cement tank]] of 1 m3 : 1 bag of cement, 100 bricks, 1 kg of wire US$ 20 * [[Plastic-lined tank volume.]] of 5 m3: US$ 50 * Sub-surface [[Classical ferrocement tank|ferro-cement tank]] of 60 m3: US$ 1,900
==Country experiences==Rainwater harvesting is a technology which is extremely flexible and adaptable to a wide variety The bigger the volume of settingsthe storage tank, it is used in the richest and poorest societies on the planet, and in lower the wettest material demand (and driest regions thus costs) for construction per m3 of the worldtank volume.
In OcaraSouthern Africa, Brazil, rainwater tanks have been constructed US$ 320 for a system with 11 m of concrete blocksgalvanized iron gutter; a 1. A low-3 m3 galvanized iron tank; downpiping; tap and filters; cost option is does not include transportation. Where roofs are not suitable for water harvesting, the [[brick cement 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, used 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 example Nicaragua planners and project staff]''. World Health Organization and GhanaIRC Water and Sanitation Centre. Geneva, Switzerland 2003.</ref>
==Manuals=Field experiences===*[http://www.irc.nl/page/37471 Download 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 book "Roofwater Harvesting: A Handbook for Practitioners" from wettest and driest regions of the IRC website]world.*[http://wwwIn Ocara, Brazil, rainwater tanks have been constructed of concrete blocks.waterland.net/showdownload.cfm?objecttype=mark.hive.contentobjects.download.pdf&objectid=1A6A3C6B* A low-F37A-BF86-37BCD14A087EE1C9 Booklet Smart Water Harvesting Solutionscost option is the [[brick cement tank]], used in for example Nicaragua and Ghana.
==Movies==Akvo RSR projects====The following projects utilize rooftop rainwater harvesting.<br>{|style="border: 2px solid #e0e0e0; width: 100%; text-align: justify; background-color: #e9f5fd;" cellpadding="2"* |- style="vertical-align: top"|[[Image:akvorsr logo_lite.png|center|60px|link=http://wwwakvo.thewaterchannelorg/products/rsr/]]|- style="vertical-align: bottom"|[[Image:project 790.tvjpg |thumb|center|140px|<font size="2"><center>[http:/index/rsr.php?optionakvo.org/en/project/790/ RSR Project 790]<br>WaSH program in <br>Rural Bangladesh</center></font>|link=com_hwdvideoshare&task=viewvideo&Itemid=53&video_id=144 Rainwater Harvesting Nepal, by BSP-Nepalhttp://rsr.akvo.org/en/project/790/]]* |[[Image:project 440.jpg |thumb|center|140px|<font size="2"><center>[http://wwwrsr.youtubeakvo.comorg/en/project/440/ RSR Project 440]<br>Raising awareness on rainwater harvesting</watch?vcenter></font>|link=QaTYxX_jajs Rooftop Rainwater http://rsr.akvo.org/en/project/440/ ]] |[[Image: rainwater harvesting India], by Zenrainman, for green schools.jpg|thumb|center|140px|<font size="2"><center>[http://wwwrsr.rainwaterclubakvo.org/en/project/2618/ RSR Project 2618], documenting the Sachetana programme of the government of Karnataka, India<br>Rainwater for Green Schools Initiative</center></font>|link=http://rsr.akvo.org/en/project/2618/ ]] *|[[Image:project 107.jpg |thumb|center|140px|<font size="2"><center>[http://wwwrsr.youtubeakvo.comorg/watch?ven/project/107/ RSR Project 107]<br>Rainwater harvesting in Guinee Bissau</center></font>|link=wWnhYIIKY0U Indian movie by CSE (wwwhttp://rsr.cseindiaakvo.org) promoting use of rainwater harvesting/en/project/107/ ]]|}<br>
===Manuals, videos, and links===
====Manuals====
* Download the book [http://www.ircwash.org/resources/roofwater-harvesting-handbook-practitioners "Roofwater Harvesting: A Handbook for Practitioners"] from IRC.
* Booklet [http://www.washdoc.info/docsearch/title/169828 Smart Water Harvesting Solutions]
* [http://www.nwp.nl/_docs/Smart-solutions-3R.spread.pdf Smart 3R Solutions]
====Videos===={{#ev:youtube|sHppepLP-pk|200|left|<center><font size="3">Rainsong video</font></center>}} {|style="border: 1px solid #fofofo; font-size: 125%"|-|{{#ev:youtube|6KaPjPospAk|200|auto|<center>Rainwater Harvesting Nepal, <br>by BSP-Nepal</center>}}|{{#ev:youtube|QaTYxX_jajs|200|auto|<center>Combating fluorosis - <br>Harvesting rooftop rainwater</center>}}|{{#ev:youtube|wWnhYIIKY0U|200|auto|<center>Rainwater harvesting, <br>Pushpam Singh</center>}} |{{#ev:youtube|SCNr2Ung0cc|200|auto|<center>Rooftop rainwater - <br>Bangalore rural district</center>}} |} ====External links====
* [http://www.rainfoundation.org Rainwater Harvesting Implementation Network (RAIN)]
* [http://practicalaction.org/energy/waterrainwater-andharvesting-sanitation/rainwater_harvesting 8 Rainwater Harvesting information on Practical Action]* [http://www.rainwaterharvesting.org 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 www.eng.warwick.ac.uk/dtu/rwh Rainwater Harvesting info on the DTU unit of University of Warwick]* [http://web.archive.org/web/20100112111544/http://www.unep.org:80/depi/rainwater / Rainwater Partnership ]* [http://wwwcseindia.org/content/catch-water-where-it-falls-toolkit-urban-rainwater-toolkit.net/ harvesting Catch Water Where It Falls - Toolkit on Urban Rainwater ToolkitHarvesting]
* [[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.