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Rainwater harvesting
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Rainwater harvesting is the gathering, or accumulating and storing, of rainwater.
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 increase ground water levels.
e are many types of systems to harvest rainwater.
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Encyclopedia
Rainwater harvesting is the gathering, or accumulating and storing, of rainwater.
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 increase ground water levels.
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 254mm of precipitation a year) To determine the amount of precipitation falling in your area, refer to .
Domestic rooftop rainwater systems
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 as pressure vessels, inline pump controllers or pressure sensitive pumps may also be required. Finally, water purifying equipment as water-purifying plants, UV-lights or distillation equipment are sometimes (depending on local conditions ) 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. 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. Depending on the degree of personal skill and preference, a more basic (regular water tank and piping) -or more advanced (e.g. pressured systems with water treatment, etc.) system is chosen.
Commercial domestic systems
Commercial systems are also made. They are offered by a variety of companies which include Rain Man & Freerain Ltd, ... Commercial rain harvesters can be obtained in both pressurized as gravity-fed systems . Greywater treatment systems are sold by companies as Water Works UK, Nubian Water Systems, BRAC Systems, ... Again, they are available in pressurised as gravity-fed systems.
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 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, 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, 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.
In India this includes Bawdis and johads, or ponds which collect the run-off from small streams in wide area.
In India, reservoirs called tankas were used to store water; typically they were shallow with mud walls. Ancient tankas still exist in some places.
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.
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 with the highest concentrations occurring in the first rain immediately after a dry spell; 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. In Brazil alum and chlorine is added to disinfect water before consumption. Appropriate technology methods, such as solar water disinfection, provide low-cost disinfection options for treatment of stored rainwater for drinking.
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 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.
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. Gaias Garden: A Guide to Home-Scale Permaculture. Vermont: Chelsea Green Publishing Company, 2000.*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.
External links
- - A case study is given to understand the basic process of collection and use of rainwater.
- - This is a free and open forum for discussion of rainwater harvesting as alternative source of water for household, garden and rainfed farming needs.
- Online digest promoting sustainable water management practices. Includes articles, case studies, discussion forum and instructions for establishing collection systems.
- - Contains resources for rainwater harvesting in the Southwestern United States and beyond.
- - India Water Portal has a comprehensive section on Rainwater Harvesting which includes case studies, courses, movies and policies.
- .
- - Water sensitive design in a private Australian home. Builder is a PhD candidate researching household decision making to adopt decentralised pro-environmental technologies.
- - A residential and commercial rainwater harvesting system design/installation firm located in Austin, Texas.
- Information about and pictures of the components used in building a rainwater harvesting system - Australian content
- Case Studies, Articles, Presentations, Webinars and Videos of Rainwater Harvesting Technologies, Applications, Products and Solutions
- : information about water Storage and other ecological systems for water supply, including rainwater harvesting
- - A starter site for India-centric RWH information.
- online rainwater harvesting community.
- Instructional website for urban home-based rainwater harvesting.
- International alliance created at the Johannesburg World Summit on sustainable development.
- International organization on rainwater harvesting.
- innovative methods and success stories
- at Texas A&M University Extension
- - CRS Ferrocement Water Tank Construction Manual.
- - Making water everybody's business.
- Appropedia:Rainwater - articles and project descriptions on Appropedia, the sustainability wiki, for project and how-to content.
- - an association for the promotion and development of innovation in rainwater harvesting.
- Rainwater Harvesting Implementation Network : focuses on field implementation of small-scale rainwater harvesting projects
- - A simple graphical representation of how a rainwater collection system works.
- Rainwater Harvesting Training in the UK
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