I am designing a digital circuit for water pump control to always top-up the over-head tank by pumping water from the sump. I am using sensors in the over-head tank. I am now wondering why shouldn't I start the motor as soon as the water level in the over-head tank drops just a little below the top. Yes this results in the pump switching rapidly, but the total running time remains practically the same. What problems may switching the pump too often create apart from the wearing of the relay used to switch it. Since the motor used in the pump is simple induction motor, I don't see how it can be harmful for the motor to be switched too often. The advantage of this scheme is that the water levels being at top provides higher pressure, and more importantly, more backup water in case the system fails or there occurs power outage.