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Rainwater harvesting

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View of a Johad at village Thathawata
View of a stepwell at Fatehpur, Shekhawati. This one featured in the movie Paheli

Rainwater harvesting is the gathering, or accumulating and storing, of rainwater. [1]

Traditionally, rainwater harvesting has been practiced in arid and semi-arid areas, and has provided drinking water, domestic water, water for livestock, water for small irrigation and a way to replenish ground water levels.

Use around the world

Currently in China and Brazil, rooftop rainwater harvesting is being practised for use for all the above purposes. 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 has 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.

In Colorado, water rights laws severely restrict rainwater harvesting -- a property owner who captures rainwater is effectively stealing it from those who have rights to take water from the watershed.[2]

Advantages in urban areas

Rainwater harvesting in urban areas can have manifold reasons. To provide supplemental water for the city's requirement, to 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.

Two residences in the city of Toronto, Canada, use treated harvested rainwater for drinking water, and reuse water (i.e. treated wastewater) for all other household water applications including toilet flushing, bathing, showers, laundry, and garden irrigation (Toronto Healthy House).

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.

Systems

A domestic rainwater harvesting system

There are many types of systems to harvest rainwater. The type used depends greatly on the purpose (domestic or industrial use) and to some extent also on physical and human considerations.

Domestic rainwater systems

System types

At the moment, 2 types of systems are generally used. These include homebrew systems 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 as pressure vessels, inline pump controllers or pressure sensitive pumps may also be required. [3] Finally, water purifying equipment 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).

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. [6] [7] [8] Depending on the degree of personal skill and preference, a more basic (regular water tank and piping) [9]) -or more advanced (eg pressured systems with water treatment, ...) -system is chosen.

Commercial domestic systems

Commercial systems are also made. They are offered by a variety of companies which include Rain Man, ... Commercial rain harvesters can be obtained in both pressurized [10] as gravity-fed systems [11]. Greywater treatment systems are sold by companies as Water Works UK, Nubian Water Systems, BRAC Systems, ... [12] Again, they are available in pressurised as gravity-fed systems.[13] [14]

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 your collection surface is washed away from (and not into) your 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 your 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 in different environments.

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.[15] In India this includes Bawdis and johads, or ponds which collect the run-off from small streams in wide area.[16][17]

In India, reservoirs called tankas were used to store water; typically they were shallow with mud walls. Ancient tankas still exist in some places.[18]

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, NOx, SOx). High levels of pesticide have been found in rainwater in Europe the highest concentrations occurring in the first rain immediately after a dry spell;[19] 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.

References

  1. ^ Definition of rainwater harvesting
  2. ^ Graywater Reuse and Rainwater Harvesting in Colorado
  3. ^ Pressurising equipment sometimes required for rainwater collection systems
  4. ^ Water treatments sometimes not needed
  5. ^ Gravity-fed system trough height difference also sometimes enough for pressured water collection system
  6. ^ Roofwater harvesting information (ebooks, ...)
  7. ^ VillageEarth Water harvesting information
  8. ^ Concrete list of DIY-rainwater harvester systems and how to build them
  9. ^ The Farm's DIY gravity-fed rainwater harvester
  10. ^ Rainman water harvesters system operation
  11. ^ Gravity-fed rain harvester
  12. ^ Other commercial rain water harvesting systems
  13. ^ Greywater systems aviable in gravity-fed as pressurised form
  14. ^ Example of gravity-fed greywater system
  15. ^ Rainwater Harvesting and Water Purification System.
  16. ^ The River maker, New Scientist, 7 September 2002. Online edition (full article by subscription)
  17. ^ Rima Hooja: "Channeling Nature: Hydraulics, Traditional Knowledge Systems, And Water Resource Management in India – A Historical Perspective"
  18. ^ Rima Hooja: "Channeling Nature: Hydraulics, Traditional Knowledge Systems, And Water Resource Management in India – A Historical Perspective"
  19. ^ It's raining pesticides, New Scientist, 3 April 1999.

Bibliography

  • Frasier, Gary, and Lloyd Myers. Handbook of Water Harvesting. Washington D.C.: U.S. Dept. of Agriculture, Agricultural Research Service, 1983
  • 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.) (ed.). Developing World Water. London: Grosvenor Press International. pp. pp 16-17. ISBN 0-946027-29-3. {{cite book}}: |editor= has generic name (help); |pages= has extra text (help)
  • 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.
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