Rainwater harvesting is the accumulation and deposition of rainwater for reuse before it reaches the aquifer. Uses include water for garden, water for livestock, water for irrigation, etc. In many places the water collected is just redirected to a deep pit with percolation. The harvested water can be used for drinking water as well if the storage is a tank that can be accessed and cleaned when needed.
Rainwater harvesting provides an independent water supply during regional water restrictions and in developed countries is often used to supplement the mains supply. Rain water harvesting provides water when there is a drought.It Helps in enriching the groundwater level.
The concentration of contaminants is reduced significantly by diverting the initial flow of runoff water to waste. Improved water quality can also be obtained by using a floating draw-off mechanism (rather than from the base of the tank) and by using a series of tanks, with draw from the last in series. The stored rainwater may need to be analyzed properly before use in a way appropriate to its safety.
System setup 
Rainwater harvesting systems can be installed with minimal skills[clarification needed]. The system should be sized to meet the water demand throughout the dry season since it must be big enough to support daily water consumption. Specifically, the rainfall capturing area such as a building roof must be large enough to maintain adequate flow. Likewise, the water storage tank should be large enough to contain the captured water.
There are three main types of companies operating in the rainwater harvesting industry: makers of water storage, makers of accessories, and integrators. Water storage companies make tanks, barrels, and underground cisterns. Accessories are added to facilitate or improve the water capturing process. Integrators are regional practitioners which install systems.
Rain water harvesting by freshwater flooded forests 
Rain water harvesting is possible by growing fresh water flooded forests without losing the income from the used /submerged land. The main purpose of the rain water harvesting is to utilize the locally available rain water to meet water requirements throughout the year without the need of huge capital expenditure. This would facilitate availability of uncontaminated water for domestic, industrial and irrigation needs.
New approaches 
Instead of using the roof for catchment, the RainSaucer, which looks like an upside down umbrella, collects rain straight from the sky. This decreases the potential for contamination and makes potable water for developing countries a potential application. Other applications of this free standing rainwater collection approach are sustainable gardening and small plot farming.
In ancient Tamil Nadu (India), rainwater harvesting was done by Chola kings. Rainwater from the Brihadeeswarar temple was collected in Sivaganga tank. During the later Chola period, the Vīrānam tank was built (1011 to 1037 CE) in Cuddalore district of Tamil Nadu to store water for drinking and irrigation purposes. Vīrānam is a 16-kilometre (9.9 mi) long tank with a storage capacity of 1,465,000,000 cubic feet (41,500,000 m3).
Rain water harvesting was done in the Indian states of Madhya Pradesh, Maharashtra, and Chhattisgarh in the olden days[when?]. Ratanpur, in the state of Chhattisgarh, had around 150 ponds. Most of the tanks or ponds were utilised in agriculture works.
Present day 
- Currently in China and Brazil, rooftop rainwater harvesting is being practiced for providing drinking water, domestic water, water for livestock, water for small irrigation and a way to replenish ground water levels. Gansu province in China and semi-arid north east Brazil have the largest rooftop rainwater harvesting projects ongoing.
- In Bermuda, the law requires all new construction to include rainwater harvesting adequate for the residents.
- The U.S. Virgin Islands have a similar law.
- In Senegal and Guinea-Bissau, the houses of the Diola-people are frequently equipped with homebrew rainwater harvesters made from local, organic materials.
- In the Irrawaddy Delta of Myanmar, the groundwater is saline and communities rely on mud-lined rainwater ponds to meet their drinking water needs throughout the dry season. Some of these ponds are centuries old and are treated with great reverence and respect.
- In the United States: until 2009 in Colorado, water rights laws almost completely restricted rainwater harvesting; a property owner who captured rainwater was deemed to be stealing it from those who have rights to take water from the watershed. Now, residential well owners that meet certain criteria may obtain a permit to install a rooftop precipitation collection system (SB 09-080). Up to 10 large scale pilot studies may also be permitted (HB 09-1129). The main factor in persuading the Colorado Legislature to change the law was a 2007 study that found that in an average year, 97% of the precipitation that fell in Douglas County, in the southern suburbs of Denver, never reached a stream—it was used by plants or evaporated on the ground. In Colorado you cannot even drill a water well unless you have at least 35 acres. In New Mexico, rainwater catchment is mandatory for new dwellings in Santa Fe. Texas offers a sales tax exemption on the purchase of rainwater harvesting equipment. Both Texas and Ohio allow the practice even for potable purposes. Oklahoma passed the Water for 2060 Act in 2012, to promote pilot projects for rainwater and graywater use among other water saving techniques.
- In Beijing, some housing societies are now adding rain water in their main water sources after proper treatment.
- In Ireland, Professor Micheal McGinley established a project to design a rain water harvesting prototype in the Biosystems design Challenge Module at University College Dublin.
- In Australia rainwater harvesting is typically used as a supplement to the reticulated mains supply, and it is mandated in many building codes. In South East Queensland, households that harvested rainwater doubled each year from 2005 to 2008, reaching 40% penetration at that time.
- In India, rain water harvesting was first introduced by Andhra Pradesh ex-Chief Minister N. Chandrababu Naidu. He made a rule that every house which is going to built in cities of that state must have a percolation pit/rainwater harvesting system. This rule increased the ground water level in good phase. After his term as Chief Minister, the next leaders neglected this system.
- In the state of Tamil Nadu, rainwater harvesting was made compulsory for every building to avoid ground water depletion. It proved excellent results within five years, and every other state took it as role model. Since its implementation, Chennai saw a 50 percent rise in water level in five years and the water quality significantly improved.
- In Rajasthan, rainwater harvesting has traditionally been practiced by the people of the Thar Desert. There are many ancient water harvesting systems in Rajasthan, which have now been revived 
- At present, in Pune (in Maharashtra), rainwater harvesting is compulsory for any new society to be registered.
- An attempt has been made at Dept. of Chemical Engineering, IISc, Bangalore  to harvest rainwater using upper surface of a solar still, which was used for water distillation
Sri Lanka 
- Rainwater harvesting has been a popular method of obtaining water for agriculture and for drinking purposes in rural homes.
- The legislation to promote rainwater harvesting was enacted through the Urban Development Authority (Amendment) Act, No. 36 of 2007.
- Lanka rainwater harvesting forum is leading the Sri Lanka's initiative.
United Kingdom 
In the United Kingdom, water butts are often found in domestic gardens to collect rainwater, which is then used to water the garden. However, the British government's Code For Sustainable Homes encourages fitting large underground tanks to new-build homes to collect rainwater for flushing toilets, washing clothes, watering the garden, and washing cars. This reduces by 50% the amount of mains water used by the home.
- In Lod, Israel, a mixed community just southeast of Tel Aviv, a rainwater harvesting school model project is underway.
- Rainwater harvesting systems are being installed in local schools for the purpose of educating schoolchildren about water conservation principles and bridging divides between people of different religious and ethnic backgrounds all while addressing the water scarcity issue that the Middle East faces.
See also 
- Atmospheric water generator
- Water conservation
- Peak water
- First flush
- Namib Desert beetle
- Freshwater swamp forest
- Deepwater rice
||This article includes a list of references, but its sources remain unclear because it has insufficient inline citations. (June 2012)|
- New Scientist, 3 April 1999.
- White, 2009
- Rain water harvesting by fresh water flooded forests
- Kim, Sun Joo. "Harvesting rainwater for more than greywater". SmartPlanet. Retrieved 7 February 2013.
- Kumar, Ro. "Collect up to 10 gallons of water per inch of rain with Rainsaucers’ latest standalone rainwater catchment". LocalBlu. Retrieved 11 February 2013.
- "Rain water Harvesting". Tamilnadu State Government, India. Retrieved 23 January 2012.
- "Believes in past, lives in future". The Hindu (India). 17 July 2010.
- "Rare Chola inscription found near Big Temple". The Hindu (India). 24 August 2003.
- "Rainwater Collection in Colorado" (PDF). Colorado water law, notices. Colorado Division of Water Resources. Retrieved 2012-03-24.
- "Criteria and Guidelines for the "Rainwater Harvesting"" (PDF). Pilot Project Program. Colorado Water Conservation Board (CWCB). January 28, 2010. Retrieved 2012-03-24.
- Johnson, Kirk (June 28, 2009). "It’s Now Legal to Catch a Raindrop in Colorado". The New York Times. Retrieved 2009-06-30. "Precipitation, every last drop or flake, was assigned ownership from the moment it fell in many Western states, making scofflaws of people who scooped rainfall from their own gutters. In some instances, the rights to that water were assigned a century or more ago."
- "82(R) H.B. No. 3391. Act relating to rainwater harvesting and other water conservation initiatives. † went into effect on September 1, 2011". 82nd Regular Session. Texas Legislature Online. Retrieved 8 February 2013.
- "State Rainwater Harvesting Statutes, Programs and Legislation". NCSL. Retrieved 7 February 2013.
- "Rain Water Harvesting in Tamil Nadu increase water level by 50%". Hindu.com. 2009-01-31. Retrieved 2012-03-24.
- "Tamil Nadu praised as role model for Rainwater Harvesting". Thehindu.com. 2011-09-29. Retrieved 2012-03-24.
- "Ancient water harvesting systems in Rajasthan". Rainwaterharvesting.org. Retrieved 2012-03-24.
- Anjaneyulu, L.; Kumar, E. Arun; Sankannavar, Ravi; Rao, K. Kesava (13 June 2012). "Defluoridation of Drinking Water and Rainwater Harvesting Using a Solar Still". Industrial & Engineering Chemistry Research 51 (23): 8040–8048. doi:10.1021/ie201692q.
- Coombes P J (2007). "Energy and economic impacts of rainwater tanks on the operation of regional water systems". Australian Journal of Water Resources 11 (2): 177–191.
- Ferguson M (2012) a 12-month rainwater tank water savings and energy use study for 52 real life installations. Ozwater12 COnference, Sydney, Australia: May 2012.
- Frasier, Gary, and Lloyd Myers. Handbook of Water Harvesting. Washington D.C.: U.S. Dept. of Agriculture, Agricultural Research Service, 1983
- Geerts, S., Raes, D. (2009). Deficit irrigation as an on-farm strategy to maximize crop water productivity in dry areas. Agric. Water Manage 96, 1275–1284
- Gould, John, and Erik Nissen-Peterson. Rainwater Catchment Systems. UK: Intermediate Technology Publications, 1999.
- Hemenway, Toby. Gaia’s Garden: A Guide to Home-Scale Permaculture. Vermont: Chelsea Green Publishing Company, 2000.
- Lowes, P. (1987). "The Water Decade: Half Time". In in John Pickford (ed.). Developing World Water. London: Grosvenor Press International. pp. 16–17. ISBN 0-946027-29-3.
- Ludwig, Art. Create an Oasis With Greywater: Choosing, Building, and Using Greywater Systems. California: Oasis Design, 1994.
- Pacey, Arnold, and Adrian Cullis. Rainwater Harvesting. UK: Intermediate Technology Publications, 1986.
- Pachpute J.S..(2010)A package of water management practices for sustainable growth and improved production of vegetable crop in labour and water scarce Sub-Saharan Africa.Agricultural Water Management.Volume 97, Issue 9, September 2010, Pages 1251-1258
- Pachpute J S, Tumbo Siza D, Sally H, Mul M L .(2009). Sustainability of Rainwater Harvesting Systems in Rural Catchment of Sub-Saharan Africa. Water Resources Management, Volume: 23, Issue: 13 (2009).
- White I. (2009). Decentralised Environmental Technology Adoption: The household experience with rainwater harvesting (PhD Thesis). Australia: Griffith University.
|Wikiversity has learning materials about Rain barrel|
|Wikibooks has a book on the topic of: Drinking of water|
|Wikibooks has more on the topic of: Rainwater harvesting|
|Wikimedia Commons has media related to: Rainwater harvesting|
- Rainwater harvesting and purification system.
- The Texas Water Development Board
- International Rainwater Harvesting Alliance (IRHA)
- Rainwater Harvesting Potential Calculator
- Rainwater Harvesting Organisation RAIN
- The mission of the American Rainwater Catchment Systems Association is to promote sustainable rainwater-harvesting practices to help solve potable, non-potable, stormwater and energy challenges throughout the world.