actually a water pumping is consuming power proportionally to the work done (water moved) and therefore indrectly proportional to the resistance (head pressure).
Run a water pump wide on with virtually no head pressure...and you get the greatest flow...and highest power consumption. Ususally the sweetspot is to run a punp with around 1/4 of the maximum head pressure. Of course if varies with brand and model. So check the flow and power consumption charts from the maker.