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RAINWATER HARVESTING

The purpose of this article is to bring light on “Various methods of Rainwater Harvesting”.

Problem

On one side we humans are telling that water is scarce and at the same time during the rainy season, we are complaining about the floods on the streets, and sometimes in some places floodwater enter the houses too.

Practice

Most of the houses in India were dependent on borewell water or government water supply. Even during the rainy season we are using water from these two sources only, and very less population is using rainwater as the source of water during the rainy season by collecting in the utensils or big plastic drums. The fixed structure can be constructed or plastic tanks can be used for the collection of rainwater.

Advantage

India was having the lowest rainfall of 50 cm in some places in a year, the house of size 100 square feet can able to collect 4645 litres of rainwater. To store this water the house will need 175 cubic feet of rectangular tank approximately with the dimension of 7ft height x 5ft length x 5ft width. By doing so, the drinking water need of a 4 member family can be satisfied for a minimum of 230 days with average individual water drinking of 5 litres per day. If the catchment area and volume of the collection tank are increased, the drinking water need for the whole year is possible.

Three ways of collecting rainwater

The rainwater can be collected in a tank at the ground level, below the ground level, and above the house.

At the ground level, the rainwater can be collected in a plastic tank or by constructing the fixed tank as per the need, in which the rainwater from the terrace can be collected. This method usually requires more space in the living area, so it applies to the houses constructed with proper open space.

Below the ground level, the rainwater can be collected by constructing an underground tank of the required size. This method does not occupy the area above the ground level. Water can be pumped for human utilization upon requirement. These two methods are applicable for the single storey as well as multi storey buildings

Above the house, the storage above the house is possible only when a house is having a minimum of two storey. So that the terrace above the second storey will act as a catchment area and the tank can be constructed on the first floor for rainwater collection. The main advantage of this method is that during the rainy season, the ground floor household members can utilize the water getting collected in the tank for human purpose without any pumping mechanism

New Strategy

The new construction of the house can combine below the ground and above the house rainwater collection method, the two ceilings should be constructed with the heigh distance of 5 feet, the space available between the ceiling can be utilized as a water tank. The basement of 5 feet is usually filled with sand, instead of filling sand it can be constructed in the form of an underground tank to collect the rainwater. By doing these two changes, water gets stored above the house as well as below the house. this will provide two advantages one is energy is saved by avoiding the pumping of water to the upper tank and sand to be filled in for the basement gets avoided.

For example, If the house is constructed in the size of 30 by 30, the catchment area of the house will be 900 square feet (that can collect 41806 litres of rainwater per season with 50 cm rainfall) and height of the tank above and below are 5 feet each, then the house would have the tank volume of 9000 cubic feet which can store rainwater of 254851 litres of water. The collection tank can collect 5 times more water than the received rainfall that ensures no water will be wasted even if there is a 5 times increase in the rainfall rate.

Precautions

To ensure the pure rainfall collected in the tank, the catchment area should be kept clean and tidy without any dirt and additional sand-pebble filter can also be installed between the catchment area and collection tank.

Conclusion

By following the appropriate method, any house could achieve water self-sufficiency for the whole year with the available rainfall. The damages due to floods will also get reduced substantially.

(This was an intuitive article written by Dr.S.Ragavan, Assistant professor, R.B.Institute of Management Studies, Ahmedabad, Gujarat)

Reference:

  1. http://www.calctool.org/CALC/other/default/rainfall
  2. https://sciencing.com/calculate-water-fill-rectangular-tank-7686198.html