All water heaters constructed using a steel tank requires a lining to protect the internal steel surfaces from corrosion. Certain linings (i.e. glass and epoxy), due to their nature, have unavoidable holes and imperfections resulting in exposure of the steel tank. As a result of this deficiency, the manufacturer will install an anode rod(s) in an attempt to delay corrosion of the steel tank. An anode rod is typically made of aluminum, magnesium or zinc, is a maintenance item that requires periodic inspection and replacement, and is often times the cause of a “rotten egg” odor to your hot water. Often referred to as a sacrificial anode rod because, over time, it slowly dissolves, sacrificing itself as it is attacked by aggressive substances in the water which would otherwise attack the steel tank through the pinholes and imperfections of the glass or epoxy lining. A cement lined steel tank on the other hand does not require an anode because of the thickness and guaranteed 100% coverage of the cement lining over all internal surfaces of the steel tank. This eliminates the need for an anode rod in a cement lined water heater, resulting in a significantly longer life compared to a glass or epoxy lined water heater. For a further discussion please click on the following link Cement Lining