The overall efficiency of a centrifugal pump is:

📖 Explanation
In the case of a centrifugal pump, the power is decreasing from the shaft of the pump to the impeller and then from the impeller to the water. The following are the important efficiencies of a centrifugal pump:

Manometric Efficiency (ηman):
It is the ratio of the manometric head to head imparted by the impeller to the water.
ηman = Hm / Vw²u² / g = gHm / Vw²u²
Mechanical Efficiency (ηm):
It is the ratio of the power available at the impeller to the power at the shaft of the centrifugal pump.
ηm = Power at the impeller / Power at the shaft = W/g(Vw²u² / 1000) / SP
Overall Efficiency (ηo):
It is defined as a ratio of the power output of the pump to the power input to the pump.
ηo = ηman × ηm