The Danco shower volume control valve is designed to help you save water when your shower is in use. This diverter allows for the water supply volume to be turned down at the shower head. Turn the knob to slow the flow of water while you lather up, shave or wash your hair. When the water is turned down to a dribble, it does offer the benefit of keeping your water warm while the shower is in use. The valve fits between the shower's head and arm.