A building with 100 sqm roof area is connected to a 72 cum rainwater collection tank

Q. A building with 100 sqm roof area is connected to a 72 cum rainwater collection tank. If the rainfall is 60 mm per hour and the loss during water storage is 20%, then the time taken to fill the tank completely is hours.

Ans: 15.0 to 15.0

Sol:

Roof Area of the building = 100 sq.m.
Rainfall is 60 mm per hour. = 0.06 m per hour.
Thus, water collection on the roof per hour = 100 × 0.06 = 6 m³ per hour.
Thus, time to fill the 72 cum storage tank without loss = 72/6 = 12 hours.
But, there is loss of 20% during water storage.
Thus, loss of water storage per hour = (20/100) × 6 = 1.2m³
Thus, water getting stored per hour = 6 – 1.2 = 4.8 m³
Thus, to fill the 72 cum capacity water storage tank the time required = 72/4.8 = 15 hours.