Moroso electric water pump drive?

If your water pump pulley doesn’t have a fan bolted to it, you wouldn’t ever see the difference if you were running it by the crank or electrically. I’m not sure about the exact efficiency calculations, but eventually it comes to the power conserved for that becomes additional load on the alternator. The biggest advantage is that it keeps the impeller at a constant speed. Engine water pumps have a fairly narrow range of rpm variance as far as peak efficiency goes.