CSLB C-36 Plumbing ContractorService, Repair, and MaintenanceMedium
A client notices a faint sulfur or 'rotten egg' smell coming from their hot water only, specifically when using the shower or hot water faucet. The cold water does not have this smell. What is the most likely cause?
- AA leak in the gas supply line to the water heater.
- BA bacterial reaction with the anode rod in the water heater tank.
- CA faulty gas igniter in the water heater.
- DSediment buildup in the hot water supply lines.
Show answer & explanationAnswer & explanation
Correct answer: B. A bacterial reaction with the anode rod in the water heater tank.
A 'rotten egg' smell (hydrogen sulfide gas) present only in hot water is a classic sign of sulfate-reducing bacteria reacting with the magnesium or aluminum anode rod inside the water heater tank. These bacteria thrive in warm, anaerobic conditions.
Why the other options are wrong
- A. A gas leak would smell like natural gas (often described as rotten eggs due to added odorants), but it would be in the air around the heater, not specifically in the hot water from the faucet.
- C. A faulty gas igniter would prevent the water heater from heating, but wouldn't cause a 'rotten egg' smell in the water itself.
- D. Sediment buildup can cause odors, but typically not the distinct 'rotten egg' smell, and it often leads to rumbling noises or reduced capacity rather than a specific sulfur smell.
Hot Water 'Rotten Egg' Smell
A distinct sulfurous odor in hot water, commonly caused by the presence of sulfate-reducing bacteria reacting with the anode rod inside a water heater.
- Smell is hydrogen sulfide gas
- Specific to hot water
- Caused by bacteria on anode rod
- Can be resolved by flushing tank, replacing anode rod, or chlorination
Memory trick: Hot water stinks? Anode rod's the link!