Anode rod (leak Preventer) is a piece of metal that sacrifices itself to protect another piece of metal. Your water heater is made of steel. Steel is highly susceptible to rust and decay. In order to prevent the steel tank from rusting and eventually leaking, anode rods are installed. To be more specific, anodes pass there electrons to the steel to protect the steel. Think of wall spackle. You have a hole in your wall from a nail. You would spread the spackle in the hole and fill it. The anode acts just like spackle. It takes its own electrons and gives them to the steel to make sure that it stays rust and decay free. Like a can of spackle, your anode will not last forever. They can be changed every few years or installed with larger rods during installation. Theoretically if you were able to change your anodes every 3 years your water heater would last 25-50 years. BUT, changing your anodes is nearly impossible once your water heater is installed. Ok, not impossible, but its very costly and better left to a trained technician.