A water heater dip tube consists of a plastic pipe installed vertically within the water-heater tank from the cold-water inlet to within a few inches of the bottom of the tank. A dip tube transfers cold water to the bottom of the tank where it can be heated. If the dip tube is cracked or broken, the cold water mixes with the hot water at the top of the tank. This results in your unwelcome early-morning shock. When this condition arises, a cracked or broken dip tube is usually to blame.