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 they first turn on the faucet. The cold water does not have this odor. What is the most common cause of this issue?
- AA reaction between bacteria in the water heater and the anode rod.
- BA decaying animal carcass in the well water supply.
- CAn accumulation of sediment in the water heater tank.
- DA leak in the gas supply line to the water heater.
Show answer & explanationAnswer & explanation
Correct answer: A. A reaction between bacteria in the water heater and the anode rod.
The 'rotten egg' smell (hydrogen sulfide gas) in hot water only is typically caused by harmless sulfate-reducing bacteria reacting with the magnesium or aluminum anode rod in the water heater, especially when the water has a high sulfate content.
Why the other options are wrong
- B. A decaying animal in a well would affect both hot and cold water and would likely produce a more pervasive and stronger odor, not just isolated to hot water.
- C. Sediment accumulation can cause rumbling noises and reduce efficiency, but doesn't typically produce a sulfur smell.
- D. A gas leak would smell like sulfur (rotten eggs) but would be present whether water is running or not, and would be a safety hazard, not isolated to hot water.
Hot Water 'Rotten Egg' Smell
A sulfurous odor in hot water, usually from sulfate-reducing bacteria reacting with the water heater's anode rod.
- Odor is hydrogen sulfide (H2S) gas, smells like rotten eggs.
- Typically isolated to hot water, especially when first run.
- Caused by anaerobic bacteria in the water heater reacting with the anode rod (often magnesium) and sulfates in the water.
Memory trick: Hot water stinks, anode rod links.