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Hot Water Smells Like Rotten Eggs? Here’s Why
Last updated October 15, 2026.
If you smell rotten eggs in the air, not just from the hot water, leave the house now and call the gas utility or 911 from outside. Gas utilities add a rotten-egg odor to natural gas. A smell only when hot water runs is a water problem.
Safety first: If you smell gas, leave now and call the gas utility or 911 from outside. If a CO alarm sounds, get everyone outside and call 911. If hot water or steam is spraying from the heater or its relief pipe, stay back. For a serious burn, call 911.
A sulfur smell only from the hot taps usually means sulfate in your water is reacting with the tank’s anode rod, often helped by bacteria, producing hydrogen sulfide. A.O. Smith’s fix is a special anode (Use & Care 100277666, p. 28).
Causes, most common first
- Sulfides plus the anode (A.O. Smith p. 28 “SMELLY WATER — Sulfides in the water — Replace the anode with a special anode”; Rheem gas Use & Care p. 21).
- Water sitting unused (vacation, a spare bathroom).
- Well water with sulfur; if cold water smells too, it’s the supply, not the heater.
Checks you can do
Run cold, then hot, at the same tap: smell only on hot points at the heater. Run hot taps for a few minutes after time away. If the house was empty two weeks or more, run a hot tap at a sink first for several minutes before the dishwasher or washer, with no flame or spark nearby: makers warn hydrogen gas can build up (Rheem gas Use & Care p. 18).
Don’t remove the anode or add bleach or chemicals to the tank. Makers say the tank needs an anode; Rheem says running without one greatly shortens tank life and voids warranty (p. 21).
Ask a licensed plumber or water heater professional to fit the anode your maker specifies.
Know exactly why not
The anode is threaded into the top of a pressurized tank; swapping it means shutting off water and gas or power, relieving pressure, and often a breaker bar. The wrong rod can void the warranty. If cold water smells too, a water treatment pro, not a heater pro, fixes it.
Start the guided check and choose Water heater, then smelly hot water.
Sources
- A.O. Smith Use & Care 100277666, p. 28
- Rheem gas Use & Care, pp. 18, 21
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Independent information, not an inspection or a confirmed diagnosis. Not attorney-reviewed and not a licensed HVAC review. support@secondwrench.co