Even if the electric water pump should work, what is the reason to use one? It would have to be less efficient. You are converting mechanical energy to electrical energy and then back to mechanical energy? There is going to be a loss at every conversion. So in the end you will be sapping more energy from your engine to power the water pump, power that could be going into your prop.

Perry;

What you say is true, but there may be something else to consider.  The engine may not (does not) always require the full amount of flow provided by the mechanical pump.  It provides enough for full time WOT operation at sea level (presumably).  So if one had suitable control for the electric pump (big IF); then other than takeoff and climb, we might have a chance to save some power with an electric pump.

Al