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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 washing clothes and in other tasks. 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).
Rainwater harvesting is an innovative alternative water supply approach anyone can use. Rainwater harvesting captures, diverts, and stores rainwater for later use. Captured rainwater is often used in landscaping, because the water is free of salts and other harmful minerals and does not have to be treated. It is also useful in attracting and providing water for wildlife.
Implementing rainwater harvesting techniques directly benefits our state by reducing demand on the water supply, and reducing run-off, erosion, and contamination of surface water.
In many communities, 30 to 50 percent of the total water is used for landscape irrigation. Capturing rainwater for use in the landscape makes efficient use of a valuable resource, reducing water bills and reducing demand on water supply.
Rainwater harvesting can also help to prevent flooding and erosion, turning stormwater problems into water supply assets by slowing runoff and allowing it to soak into the ground. Reducing run-off also helps to reduce the contamination of surface water with sediments, fertilizers, and pesticides in rainfall run-off.
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.