An anode rod is a metal rod, typically magnesium or aluminum, threaded into the top of a storage tank water heater. It corrodes sacrificially, drawing corrosive action away from the tank's steel shell and glass lining. Once the rod is consumed, the tank itself begins to rust, which ends in leaks and replacement.
Why it matters to you
A tank water heater usually fails from the inside out, and a spent anode rod is one of the most common reasons a tank leaks before its time. Checking it during routine water heater maintenance is far cheaper than an unplanned replacement after a basement or garage floods.
Practical guidance
Have the anode rod inspected every few years during a tank flush and replaced if it is heavily eroded. Rusty or discoloured hot water, or a rotten-egg smell from the hot side only, are worth a technician's look.