The water-level switch regulates your washer's fill volume. This switch is usually a diaphragm device with a small, clear tube attached between the switch and the bottom of the washer's outer tub. As the water level in the tub increases, the pressure on the air in the tube increases. When the pressure reaches a certain level, it activates the switch, shuts off the water, and signals the timer to begin the agitate cycle. If the switch is defective, it may prematurely signal the water to shut off. If so, you probably need to replace the water-level switch. For the correct part I would need greater detail on your exact machine model.