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general information

rainwater harvesting is a technique used for collecting, storing and using rainwater for landscape irrigation and other uses. The rainwater is collected from various hard surfaces such as rooftops and/or other manmade aboveground hard surfaces.

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This ancient practice is growing in popularity due to interest in reducing the consumption of potable water and the inherent qualities of rainwater. This website will focus on general information about rainwater harvesting systems, rainwater system advantages and disadvantages, and helpful links and references.

rainwater harvesting basic components

rainwater systems come in all shapes and sizes, from simple catchment system under a downspout to large above and/or underground cisterns with complex filtration systems that can store thousands of gallons of water. Most rainwater collection systems are comprised of the same basic components catchment surface rooftop or other raised solid surface. The best catchment systems have hard, smooth surfaces such as metal roofs or concrete areas. The amount of water harvested depends on the quantity of rainfall, the size of the surface and the slope of the catchment area.

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They channel water from the catchment.area to a holding container such as a barrel, cistern or planted area leaf screens a screen that removes or catches debris. roof washers a device that diverts the first flush of rain before it enters the storage tank. Most rainwater suppliers recommend that the first flush of water is diverted to an outside area of the storage system since the catchment surface may accumulate bird droppings, debris and other pollution.

storage tanks in general, the storage tank is the most expensive component of a rainwater harvesting system. Storage containers can be made from galvanized steel, wood, concrete, clay, plastic, fiberglass, polyethylene, masonry and more. Examples of aboveground storage include cisterns, barrels, tanks, garbage cans, aboveground swimming pools and more. Storage tank prices vary based on variables such as size, material and complexity. To inhibit the growth of algae, storage tanks should be opaque and preferably placed away from direct sunlight.

The tanks should also be placed close to the area of use and supply line to reduce the distance over which the water is delivered. Also consider placing the storage on an elevated area to take advantage of gravity flow. The tank should always be placed on a stable and level area to prevent it from leaning and possibly collapsing. delivery systems gravity fed or pumped to the landscape or other end use areas. purification/treatment system needed for potable systems to make the water safe for human consumption. Please check with your local health department for information on filtration systems and certification requirements. Information is available at the county of san diego department of environmental health small drinking water systems.

general description ainwater harvesting is a technology used for collecting and storing rainwater from rooftops, the land surface or rock catchments using simple techniques such as jars and pots as well as more complex techniques such as underground check dams. The techniques usually found in asia and africa arise from practices employed by ancient civilizations within these regions and still serve as a major source of drinking water supply in rural areas. Commonly used systems are constructed of three principal components namely, the catchment area, the collection device, and the conveyance system. A catchment areas rooftop catchments: in the most basic form of this technology, rainwater is collected in simple vessels at the edge of the roof. Variations on this basic approach include collection of rainwater in gutters which drain to the collection vessel through down pipes constructed for this purpose, and/or the diversion of rainwater from the gutters to containers for settling particulates before being conveyed to the storage container for the domestic use. As the rooftop is the main catchment area, the amount and quality of rainwater collected depends on the area and type of roofing material. Reasonably pure rainwater can be collected from roofs constructed with galvanized corrugated iron, aluminium or asbestos cement sheets, tiles and slates, although thatched roofs tied with bamboo gutters and laid in proper slopes can produce almost the same amount of runoff less expensively gould, 1992.

Similarly, roofs with metallic paint or other coatings are not recommended as they may impart tastes or colour to the collected water. Roof catchments should also be cleaned regularly to remove dust, leaves and bird droppings so as to maintain the quality of the product water see figure 1. Land surface catchments: rainwater harvesting using ground or land surface catchment areas is less complex way of collecting rainwater.

It involves improving runoff capacity of the land surface through various techniques including collection of runoff with drain pipes and storage of collected water. Compared to rooftop catchment techniques, ground catchment techniques provide more opportunity for collecting water from a larger surface area. By retaining the flows including flood flows of small creeks and streams in small storage reservoirs on surface or underground created by low cost e.g. There is a possibility of high rates of water loss due to infiltration into the ground, and, because of the often marginal quality of the water collected, this technique is mainly suitable for storing water for agricultural purposes. Various techniques available for increasing the runoff within ground catchment areas involve: i clearing or altering vegetation cover, ii increasing the land slope with artificial ground cover, and i reducing soil permeability by the soil compaction and application of chemicals see figure 2. Clearing or altering vegetation cover: clearing vegetation from the ground can increase surface runoff but also can induce more soil erosion.

Use of dense vegetation cover such as grass is usually suggested as it helps to both maintain an high rate of runoff and minimize soil erosion. Increasing slope: steeper slopes can allow rapid runoff of rainfall to the collector. However, the rate of runoff has to be controlled to minimise soil erosion from the catchment field. Use of plastic sheets, asphalt or tiles along with slope can further increase efficiency by reducing both evaporative losses and soil erosion.

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The use of flat sheets of galvanized iron with timber frames to prevent corrosion was recommended and constructed in the state of victoria, australia, about 65 years ago kenyon, 1929 cited in unep, 1982. Soil compaction by physical means: this involves smoothing and compacting of soil surface using equipment such as graders and rollers. To increase the surface runoff and minimize soil erosion rates, conservation bench terraces are constructed along a slope perpendicular to runoff flow. The bench terraces are separated by the sloping collectors and provision is made for distributing the runoff evenly across the field strips as sheet flow. Soil compaction by chemical treatments: in addition to clearing, shaping and compacting a catchment area, chemical applications with such soil treatments as sodium can significantly reduce the soil permeability. Use of aqueous solutions of a silicone water repellent is another technique for enhancing soil compaction technologies.