When you combine water and metal, what do you get? You probably thought “rust,” but that’s not necessarily true. For corrosion to occur in metal (rust is a type of corrosion), it must be in contact with metal in the presence of oxygen. If you’ve ever wondered why your water heater—a metal device that holds water—doesn’t rapidly rust, the reason is that water heaters are designed to remove oxygen and/or direct contact between metal and water.
This doesn’t mean water heaters are impervious to corrosion. Far from it. Lack of maintenance can lead to corrosion setting in early on a water heater. But even with rigorous maintenance, a water heater can start to rust when it gets old enough. Does the appearance of rust mean that a water heater is done and needs to be replaced?