Definitely the wrong approach for any pumping any liquid. The current needed to accelerate the motor, pump and the fluid from rest to movement is many, many times what is required to maintain the flow.
In addition, pumps are designed to operate at a certain speed and are much less efficient running slower or faster than that speed.
Exactly what control are you attempting to create?
Water pump control is normally done by running the pump at correct speed, but feeding the output back into the input, so you have a loop of water under pressure. Then have a valve to take the water under pressure from the loop to go to wherever you need it.
Then you have consistent flow because the pressure is constant.
Paul