Water is the essential need of living being. Rainwater is the purest form of water and we should store this water for our future use.
To be specific :
1000 Sq.ft. of land can save 1 lakh litre water per year.
For example :
In Nagpur city, per year rainfall is 1100mm and the roof area is 1000 Sq.ft. So amount of rain water harvested is 1,10,000 litres .This water can be stored in the tank and surplus will be passed to the ground for increasing water level.
In Mumbai city, per year rainfall is 1800mm and roof area is 2000 Sq. ft. So amount of rain water harvested is 3,60,000 litres. So this stored water can be use in future when needed and does not want to depend on others.
The approx. cost for 1000 Sq. ft. is 10,000 Rs.