A hot water heater anode is a rod, often made of magnesium, found inside the water heater's tank. The anode prolongs the life of the water heater by diverting corrosive forces away from the lining of the tank. It is also called a sacrificial anode.
There are a number of different types of anodes. Magnesium anodes are the most common, but there are also aluminum anodes, hybrid anodes and even powered anodes. Anodes are available for purchase at hardware stores and online retailers. To ensure the longevity of a water heater, anodes require regular inspection and replacement about every five years.