Harvest rainwater
Regardless of their sophistication, rainwater harvesting systems generally have four common components:
- A catchment area for rainfall interception;
- A cistern for rainwater storage;
- A conveyance between the catchment and cistern; and
- Some method to draw upon the storage for consumptive use.
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[edit] What is Rainwater Harvesting?
Rainwater harvesting is the accumulating and storing, of rainwater. It has been used to provide drinking water, water for livestock, water for irrigation or to refill aquifers in a process called groundwater recharge. Rainwater collected from the roofs of houses, tents and local institutions, or from specially prepared areas of ground, can make an important contribution to drinking water. In some cases, rainwater may be the only available, or economical, water source. Rainwater systems are simple to construct from inexpensive local materials, and are potentially successful in most habitable locations. Roof rainwater can be of good quality and may not require treatment before consumption. Although some rooftop materials may produce rainwater that is harmful to human health, it can be useful in flushing toilets, washing clothes, watering the garden and washing cars; these uses alone halve the amount of mains water used by a typical home. Household rainfall catchment systems are appropriate in areas with an average rainfall greater than 200 mm (7.9 in) per year, and no other accessible water sources (Skinner and Cotton, 1992).
There are a number of types of systems to harvest rainwater ranging from very simple to the complex industrial systems. Generally, rainwater is either harvested from the ground or from a roof. The rate at which water can be collected from either system is dependent on the plan area of the system, its efficiency, and the intensity of rainfall (i.e annual precipitation (mm per annum) x square meter of catchment area = litres per annum yield) ... a 200 square meter roof catchment catching 1,000mm PA yields 200 kLPA.
[edit] Ground catchment systems
Ground catchments systems channel water from a prepared catchment area into storage. Generally they are only considered in areas where rainwater is very scarce and other sources of water are not available. They are more suited to small communities than individual families. If properly designed, ground catchment systems can collect large quantities of rainwater.
Rainwater harvesting systems channel that falls on to a roof into storage via a system of gutters and pipes. The first flush of rainwater after a dry season should be allowed to run to waste as it will be contaminated with dust, bird droppings etc. Roof gutters should have sufficient incline to avoid standing water. They must be strong enough, and large enough to carry peak flows. Storage tanks should be covered to prevent mosquito breeding and to reduce evaporation losses, contamination and algal growth. Rainwater harvesting systems require regular maintenance and cleaning to keep the system hygienic.
[edit] Subsurface dyke
A subsurface dyke is built in an aquifer to obstruct the natural flow of groundwater, thereby raising the groundwater level and increasing the amount of water stored in the aquifer.
The subsurface dyke at Krishi Vigyan Kendra, Kannur under Kerala Agricultural University with the support of ICAR, has become an effective method for ground water conservation by means of rain water harvesting technologies. The sub-surface dyke has demonstrated that it is a feasible method for conserving and exploiting the groundwater resources of the Kerala state of India. The dyke is now the largest rainwater harvesting system in that region.
[edit] Groundwater recharge
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 the 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.
[edit] Advantages in urban areas
Rainwater harvesting can (a) assure an independent water supply during mains water restrictions, that is (b) though somewhat dependent on end use and maintenance, usually of acceptable quality for household needs and (c) renewable at acceptable volumes despite forecast climate change (CSIRO, 2003). It produces beneficial externalities, (d) reducing peak stormwater run off and processing costs. RH systems are (e) simple to install and operate, (f) running costs are negligible and (g) convenient by providing water at the point of consumption.
Rainwater harvesting can be adopted in cities are to provide supplemental water for the city's requirements, to increase soil moisture levels for urban greenery, to increase the water table through artificial recharge, to mitigate urban flooding and to improve the quality of groundwater. In urban areas of the developed world, at a household level, non-potable uses of harvested rainwater include bathroom (i.e. shower/bath/basin), flushing toilets and washing laundry. Indeed in hard water areas it is superior to mains water for this, reducing deamnd on detergents and soaps. Rainwater may require treatment prior to use for drinking, depending on anthropogenic (e.g. vehicle exhaust) and natural (e.g. eColi.) issues.
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 faeces, 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 the 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. So-called "appropriate technology" methods, such as solar water disinfection, provide low-cost disinfection options for treatment of stored rainwater for drinking.
[edit] System sizing
It is important that the system is sized to meet the water demand throughout the dry season. Generally speaking, the size of the storage tank should be big enough to meet the daily water requirement throughout the dry season. In addition, the size of the catchment area or roof should be large enough to fill the tank.
[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 Rajasthan, India rainwater harvesting has traditionally been practiced by the people of the Thar Desert.
- 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 the Indus Valley Civilization, Elephanta Caves and Kanheri Caves in Mumbai rainwater harvesting alone has been used to supply in their water requirements.
- 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 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 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.
- 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 Utah, collecting rainwater from the roof is illegal unless the roof owner also owns water rights on the ground. In New Mexico, rainwater catchment is mandatory for new dwellings in Santa Fe.
- Kerala, India,
- In Australia rainwater harvesting is typically used to supplement the reticulated mains supply. In south east Queensland, households that harvested rainwater doubled each year from 2005 to 2008, reaching 40% penetration at that time (White, 2009 (PhD)).
[edit] See also
[edit] Rainwater Harvesting step by step
- Technologies for Rainwater harvesting
- Rooftop harvesting
- Gutters and downpipes
- Tanks or reservoirs
- Designing a system
- Planning and management
[edit] Links
- See WELL FACTSHEET Domestic Rainwater Harvesting
- Homeowner's guide to rainfall Instructional website for urban home-based rainwater harvesting
- Rainwater harvesting guide
- Rainharvesting Systems
- Low Impact Factsheet Rainwater harvesting
- Recycled Whiskey Rain Barrels
- Oasis Rainwater Harvesting Tanks and Systems
