### 1. Dear B. M. Singh, For

Dear B. M. Singh,

For calculating the horse power of the pump for lifting the water to roof top, it will be required to do the following:

• The important parameters are the amount of water to be lifted (discharge) and the head from location of the pump to the roof top and the time in which, we want to lift the requisite quantity of water.
• Calculate the discharge of water to be lifted. For example ,if the per capita consumption is 200 lpcd, the days consumption will work out to  1000 liters or 1m3 and if it were to be lifted in 15 minutes, the requisite discharge will work out to (1m3/ (15*60)sec. or (1/900) m3/sec
• The formula for calculating the HP of the pump is (Q*1000*h)/ (75*eff) where is Q is the discharge in cum/sec; 1000 is the specific wt of water and h is the lift calculated from the location of the pump to the roof top. For a 3 storey building it would be 10 to 11 m. eff is the efficiency of the pump.
• By applying the above the requisite HP for the example above would work out to 0.25 HP, with a pump efficiency of 70%. However the next issue would be to see what capacity pumps are available in the market, which may be usually more than 0.25 HP. The same should be procured.

With regards,

Vijay Kumar

Hydrologist