Rainwater harvesting is a way of catching rain, filtering it, and using it for drinking and non-drinking purposes. It can be done using rooftop gutters or underground pipe systems.
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Rooftop Rainwater Harvesting
As water comes down a roof, it flows down into the roof-top gutter. Water flows through this gutter to a pipe which leads to a drum that acts as a filter. A pipe from the drum takes the water to the storage tanks. As the first 15 minutes of rain washes the roof, it must not be collected. Therefore, the pipe from the drum joins the tank not at the bottom of the drum but higher up along the side. Water from the storage tank is pumped up to the overhead tank where the whole house gets its water.
The photographs below show how rooftop rainwater harvesting is done in a house in Kodaikanal, India.
Pipe leading from filter drum to storage tank
These photographs are courtesy of Mr. K. Balakrishnan who harvests rainwater efficiently at his house. With a roof of 200m2, each mm of rain gets him 200m2 X 1/1000m = 0.2 m3 = 200 litres of water.
Underground System of Rainwater Harvesting
Another way to harvest rainwater is to catch rain falling on the ground. In a brick tank, rainwater can be filtered through different layers of material such as sand, gravel, and charcoal. Pipes with fine holes on the top (called 50 mm perforated pipes) are placed below the filter. When rain falls, these pipes soak up the filtered water which is collected and sent to an overhead tank. Water from the overhead tank can be used by residents of the building. The filtered water can also be sent into a well. In a dry country, doing this can increase a well’s life by up to 2 ½ months in the hot summer.
Here is a diagram of the underground system of rainwater harvesting.
Rain water harvesting is a free, easy, efficient and environmentally friendly way of collecting water. Remember a drop of water not wasted is a drop saved!
Singapore: An Example of Rainwater Harvesting
Most of Singapore’s population lives in high rise buildings. Almost all buildings are fitted with gutters to catch the rain. The water that falls on roads flows into storm drains. These drains are connected together in an island-wide system, where the largest drains are 5-6 meters wide. These storm drains carry the water to reservoirs to be filtered. This is how 96% of the rain water is caught, cleaned, and re-used. Water falling on rooftops is also collected for non-drinking uses
Surprisingly, one of the main water harvesting places is at Changi airport! Here, all the water on the runway is caught and sent to reservoirs. Water collected in this way is used for non-drinking purposes such as fire-fighting drills and flushing toilets. The airport meets nearly one-third of its water requirements from harvested rainwater, saving $390,000 per year.
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Source : Information obtained by talking to two experts, Mr. K. Balakrishnan and Mr. John Raju, in this area (December - January 2006-2007).
"Rainwater Harvesting And Utilisation." United Nations Environment Programme 28 February 2007 <http://www.unep.or.jp/ietc/Publications/Urban/UrbanEnv-2/9.asp>.
Diagram of underground system of rainwater harvesting created by Arun (website author).
Photographs are used with the permission of Mr. K. Balakrishnan.
Flash movie created by author of this web page. Permission to use all images of rainwater harvesting is granted by Mr. Balakrishnan. Image of rainwater on umbrella is granted under the terms of the GNU Free Documentation License from Wikipedia, the Free Encyclopedia. January-February 2007 <http://en.wikipedia.org/wiki/Main_Page>.
All music used in the movie is royalty free from Royalty Free Music.com. March, 2007 <http://www.royaltyfreemusic.com/free.html>.
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