Anode rods protect the lining of water heater tanks from corrosion. In rare instances, anode rods can contribute to foul-smelling hot water that has the odor of rotten eggs. This may occur when there are high sulfur and low oxygen concentrations in supply water. The anode rod promotes the generation of hydrogen which, along with sulfur-eating bacteria, is the final cause of the smell.
Removing the anode rod may be the easiest fix for this problem, but doing so shortens the life of the tank and voids the warranty on most models. Many manufacturers offer specially-designed aluminum/zinc anode rods that, along with chlorination of the unit, minimize the unpleasant smell. A.O. Smith units require a KA-90 anode rod to fight the rotten egg odor, while Bradford White recommends A420 anode rods. These are the water heater brands SupplyHouse.com carries.