How
much water can be harvested?
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The following is on illustrative calculation
that highlights the enormous potential for rainwater harvesting.
The same procedure can be applied to get the potential for any land
of or rooftop area. using rainfall data for that area.
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Consider a building with a flat terrace
area of 100 sq.m. The average annual rainfall in chennai is proximately
1100 mm (44 inches). In simple terms, this means that if the terrace
floor is assumed to be impermeable, and all the rain that falls
on it is retained without evaporation, then, in one year, there
will be rainwater on the terrace floor to a height of 1100mm.
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| Area of plot |
= 100sq.m. |
| Height of rainfall |
= 1.1.(1100 mm or 44 inches) |
| Volume of rainfall over the plot |
= Area of plot x Height of rainfall |
| |
= 100 sq.m. 1.1cu.m.110 cu.m.(1.10.000 liters) |
| Assuming that only 60% of that total rainfall
is effectively harvested. |
| Volume of water harvested |
= 66,000 liters |
This volume is about four times the annual
drinks water requirement of a five member family. The average dally
water requirement per person is 10 liters according to IS172: Indian
standard code of Basic Requirement for Water Supply, Drainage and
Sanitation.
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