Run the cold tap too. If the cold water is discolored as well, the cause is the water supply or plumbing, not the heater.
Likely causes
- Iron bacteria in the water, the most common cause per A.O. Smith; treated with shock chlorination.
- A depleted anode rod, after which the tank begins to corrode.
- Rarely, a failing tank lining.
Checking the anode rod
A.O. Smith recommends inspecting the anode within three years and then every year, or yearly from the start if you use softened water. Its warranty excludes replacement for discolored or rusty water, so maintenance is on the owner.
When to replace the heater
Rust on the outside of the tank, especially at the bottom, or water leaking from the tank body means the tank has failed.
General information, not professional or legal advice; follow your manufacturer's manual, and your installer and local permit office have the final word. Sources:A.O. Smith Technical Bulletin 21 (discolored water); A.O. Smith residential electric water heater manual (185762).
Water Heater Replacement in San Diego →