Rainwater harvesting

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Rainwater harvesting is the gathering, or accumulating and storing, of rainwater.^[1] Rainwater harvesting has been used to provided household drinking water, water for livestock, water for irrigation and a way to refill aquifers in a process called groundwater recharge.

Contents 1 Systems 2 Domestic rooftop rainwater systems 2.1 System types 2.1.1 DIY domestic systems 2.1.2 Commercial domestic systems 3 Subsurface dyke 3.1 System's operation 4 Industrial systems 5 Advantages in urban areas 6 Quality 7 Around the world 8 References 9 Bibliography 10 External links

[edit] Systems

There are many types of systems to harvest rainwater. Notable systems are systems for runoff rainwater (eg hillside run-off) and rooftop rainwater harvesting systems. The type used depends greatly on the purpose (domestic or industrial use) and to some extent also on economics and physical and human considerations. Generally speaking, rooftop rainwater systems are most used as they are most economical (if there is more than 254 mm of precipitation a year)^[2]

[edit] Domestic rooftop rainwater systems

[edit] System types

At the moment, 2 types of systems are generally used. These include DIY and commercial systems. Both of these systems are known under the term water harvesters and require only a limited amount of knowledge to set up (if basic systems are used). In both cases, the system consists of a storage tank to store the water and piping (to guide the water in). Additionally, extra pressuring equipment such as pressure vessels, inline pump controllers or pressure sensitive pumps may also be required. ^[3] Finally, water purifying equipment such as water-purifying plants, UV-lights or distillation equipment are sometimes (depending on local conditions ^[4] ) added to purify the collected water. The system is then called a Greywater treatment system. Greywater systems are usually preferred over regular water harvesters as they allow the system to not only treat the rainwater, but water from other sources as well (eg the watercloset; if plants are used). However, this feature may also be averted by using a UV-lamp and composting toilet instead.

Depending on local circumstances, a gravity-fed system may already be enough to have a pressured water collection system. ^[5] In the latter case, no pumps/pressure vessels are thus required to have a pressured system. In practice, gravity-controlled systems are usually created by placing the water harvester on an elevation (eg rooftops).

[edit] DIY domestic systems

As water conservation is becoming more and more popular, more people have begun to make their own homebrew installation. These systems range from traditional technologies like rain barrels to more complex greywater systems. Through the Internet, plans and accurate construction information have become available. Depending on the degree of personal skill and preference, a more basic (regular water tank and piping^[6]) -or more advanced (e.g. pressured systems with water treatment, etc.) system is chosen.

[edit] Commercial domestic systems

Commercial systems are also made. They are offered by a variety of companies ... Commercial rain harvesters can be obtained in both pressurized ^[7] as gravity-fed systems ^[8].

[edit] Subsurface dyke

Subsurface dyke is a structure that is built in an aquifer with the intention of obstructing the natural flow of ground water, thereby raising the ground water level and increasing the amount of water stored in the aquifer.

The subsurface dyke constructed at Krishi Vigyan Kendra, Kannur under Kerala Agricultural University with the support of ICAR as part of demonstrating rain water harvesting technologies has become a living example for an effective method for ground water conservation. The success story of the sub-surface dyke has demonstrated that it is one of the most feasible methods for the conservation and exploitation of the ground water resources of the state. The dyke is now the largest rainwater harvesting system in the region.

[edit] System's operation

A mechanism can be used to send the initial water flow to waste, usually the first few liters. These are commonly known as 'first-flush' diverters, and are used to increase the chance that the large-particle residue that might accumulate on a collection surface is washed away from (and not into) the storage tank. Such a system also compensates for the fact that the initial minutes of a rainfall can include airborne pollutants being washed from the sky^{[citation needed]}, and likewise minimizes contamination of the captured supply. Simple but regular inspection and maintenance of such a device is usually necessary.

Not all catchment systems use such a feature. For example, rainwater in rural areas of Australia is traditionally used without such a system, and without treatment,^{[citation needed]} but this may be unwise^[vague] in different environments.

[edit] Industrial systems

Rainwater may also be used for groundwater recharge, where the runoff on the ground is collected and allowed to be absorbed, adding to the groundwater. In US, rooftop rainwater is collected and stored in sump.^[9] In India this includes Bawdis and johads, or ponds which collect the run-off from small streams in wide area.^[10][11]

In India, reservoirs called tankas were used to store water; typically they were shallow with mud walls. Ancient tankas still exist in some places.^[12]

[edit] Advantages in urban areas

Rainwater harvesting in urban areas can have manifold reasons. To provide supplemental water for the city's requirement,it increase soil moisture levels for urban greenery, to increase the ground water table through artificial recharge, to mitigate urban flooding and to improve the quality of groundwater are some of the reasons why rainwater harvesting can be adopted in cities. In urban areas of the developed world, at a household level, harvested rainwater can be used for flushing toilets and washing laundry. Indeed in hard water areas it is superior to mains water for this. It can also be used for showering or bathing. It may require treatment prior to use for drinking

In New Zealand, many houses away from the larger towns and cities routinely rely on rainwater collected from roofs as the only source of water for all household activities. This is almost inevitably the case for many holiday homes.

[edit] Quality

As rainwater may be contaminated, it is often not considered suitable for drinking without treatment. However, there are many examples of rainwater being used for all purposes — including drinking — following suitable treatment.

Rainwater harvested from roofs can contain animal and bird feces, mosses and lichens, windblown dust, particulates from urban pollution, pesticides, and inorganic ions from the sea (Ca, Mg, Na, K, Cl, SO₄), and dissolved gases (CO₂, NO_x, SO_x). High levels of pesticide have been found in rainwater in Europe with the highest concentrations occurring in the first rain immediately after a dry spell;^[13] the concentration of these and other contaminants are reduced significantly by diverting the initial flow of water to waste as described above. The water may need to be analysed properly, and used in a way appropriate to its safety. In Gansu province for example, harvested rainwater is boiled in parabolic solar cookers before being used for drinking.^{[citation needed]} In Brazil alum and chlorine is added to disinfect water before consumption.^{[citation needed]} Appropriate technology methods, such as solar water disinfection, provide low-cost disinfection options for treatment of stored rainwater for drinking.

[edit] Around the world

• 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 Indus Valley Civilization, Elephanta Caves and Kanheri Caves in Mumbai rainwater harvesting alone has been used to supply in their water requirements.

• In Senegal/Guinea-Bissau, the houses of the Diola-people are frequently equipped with homebrew rainwater harvesters made from local, organic material.

• In the United Kingdom water butts are oft-found in domestic gardens to collect rainwater which is then used to water the garden.

• Up until 2009 in Colorado, water rights laws restrict rainwater harvesting, a property owner who captured rainwater was stealing it from those who have rights to take water from the watershed. In Utah and Washington State, collecting rainwater from the roof is illegal unless the roof owner also owns water rights on the ground. In New Mexico rainwater catchmentis mandatory for new dwellings in Santa Fe.^[14]

[edit] References

[edit] Bibliography

• 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. 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.

[edit] External links

This article's external links may not follow Wikipedia's content policies or guidelines. Please improve this article by removing excessive or inappropriate external links. (April 2009)

Wikibooks has more on the topic of Rainwater harvesting

• [1] – *[2] India's first and most extensive website on rainwater harvesting having case studies, toolkit, data, animations, news articles, online query on both rural and urban rainwater harvesting.
• rwhdigest.com – Online digest promoting sustainable water management practices. Includes articles, case studies, discussion forum and instructions for establishing collection systems.
• RWH on India Water Portal - India Water Portal has a comprehensive section on Rainwater Harvesting which includes case studies, courses, movies and policies.
• Rainwater harvesting System set-up information from Appropedia.
• Akash Ganga RWH - A starter site for India-centric RWH information.
• Rainwater Harvesting at Texas A&M University Extension
• Appropedia:Rainwater - articles and project descriptions on Appropedia, the sustainability wiki, for project and how-to content.