Question: If water causes steel to rust, why doesn’t the inside of my water heater tank rust out?
Answer: It will eventually, unless you have a working anode rod installed.
What is a water heater anode rod?
It’s a fact of nature that water corrodes many kinds of metals—steel most noticeably. But here’s where a bit of cleverness comes in with the invention of the water heater. If you introduce a rod of more “tempting” (that is, more easily corroded) metal into the environment, the water will react with that and leave the steel unaffected.