Water heater anode rod or sacrificial anode is the important component part with only one purpose; to protect metal tank from corrosion.
Most hot water heaters are equipped with one or more anode rods. Anode service depends on the water conductivity as the rod deteriorates during the time. This is why it is important to maintain the rod, to keep the tank in operating condition. Depleted anode rod does not affect the water taste or color but the rod inspection and replacement can extend the life of your heater.