Electricity is needed for the pump and the heating. The pump current can be neglected. What really needs electricity is the water heating. And here physics applies. It always takes the same amount of energy to heat a certain mass of water by 1°. So either you are in a hurry and need a large current flow in a short time, or it takes longer with a smaller current flow. Therefore, these statements by "kmuinformatiker" are not coherent.