What effect does a worn impeller have on the energy needed to pump the same volume of water?

A worn impeller affects the efficiency of a pump, which in turn directly impacts the energy required to move a certain volume of water. When an impeller is worn, it becomes less effective at converting the mechanical energy supplied by the motor into hydraulic energy for moving water. This inefficiency means that more energy is needed to achieve the same flow rate compared to a new or well-maintained impeller.

As the wear progresses, the hydraulic losses increase due to factors like reduced flow capacity and increased turbulence. The pump has to work harder, which translates to higher energy consumption. Therefore, the need for increased energy to pump the same volume of water is a direct result of the reduced performance of a worn impeller and is accurately represented by the chosen answer.