Anodes in a water heater are divided into sacrificial anode rods and titanium anode rods. A sacrificial anode rod is an exposed metal rod that is inserted into the water heater. It is designed to corrode slowly over time. The sacrificial anode is made from either magnesium, aluminum, or zinc. The lifespan of sacrificial anodes varies greatly based on local water conditions and quality. Annual inspection and replacement for sacrificial anode rods are recommended. In areas with sulfides in the water, there is a reaction with magnesium anodes which creates hydrogen sulfide gas that creates a rotten egg smell in the water. In areas with high conductivity water, aluminum anodes are depleted too quickly, leaving the tank unprotected.