Water circulating through a hot water circulation system becomes chemically inert and does not rust the piping. But
water heaters have a constant supply of fresh water with lots of corrosion-causing oxygen. Because of this, water
heaters are prone to corrosion. As a result, water heaters usually have an anti-corrosion rod or sacrificial rod
installed. Sacrificial anodes are typically made of magnesium or aluminum. The rod is immersed inside the water
heater tank, allowing the chemical reaction from the fresh water to attack it rather than the tank. In some areas,
rods are replaced regularly.