Dip tube
The long tube that sends incoming cold water to the bottom of the tank.
Cold water enters a tank water heater through a long plastic dip tube that carries it down to the bottom, so the burner or lower element heats it and the hottest water stays at the top where the outlet draws from. If the dip tube cracks, breaks, or crumbles, cold water dumps in near the top instead and blends straight into the hot water heading to your taps — so showers turn lukewarm and then cold far sooner than they should. A failed dip tube is one of the most common reasons hot water [runs out too fast](/guides/hot-water-runs-out-too-fast).