Short answer
If only the hot water smells, the usual cause is hydrogen sulfide made inside the tank: sulfate-reducing bacteria in the water react with hydrogen generated by the magnesium anode rod. The common fix is to disinfect the tank with chlorine and swap the anode for a different type. Never remove the anode entirely; that voids the warranty.
Key facts
- Bradford White says the odor needs three things: sulfur, hydrogen and bacteria. The magnesium anode supplies enough hydrogen to complete the reaction.[1]
- Bradford White's procedure uses 1/2 to 1 gallon of bleach left in the tank for at least 3 hours, ideally a full day, before flushing.[1]
- Removing the anode entirely voids the warranty and shortens tank life, per Bradford White.[1]
First: is it in the water or in the air?
This page is about a smell that comes out of the hot tap. If you smell rotten eggs or sulfur in the air near the water heater, furnace, stove or meter, treat it as a gas leak. Natural gas carries an added odorant that smells like rotten eggs. Leave on foot, avoid anything that can spark, and call the gas utility and 911 from a safe place[3]. See gas smell near the water heater.
A two-minute test
Run the cold tap in the kitchen, then the hot tap. Smell each in a glass.
| What you find | What it points to |
|---|---|
| Only the hot water smells | Reaction inside the water heater (this page) |
| Hot and cold both smell | Sulfur in the water supply itself, common with private wells. Test the water |
| Smell only at one sink | Bacteria in that drain, not the water. Smell the water in a glass away from the sink |
| Smell in the air near gas appliances | Possible gas leak. Leave and call |
Why it happens inside the tank
Every steel tank water heater has a sacrificial anode rod, a metal rod that corrodes so the tank lining does not. Many tanks ship with magnesium anodes. Bradford White explains the chemistry plainly: the odor needs sulfur, hydrogen and bacteria. Some water supplies carry sulfur compounds and sulfate-reducing bacteria. The magnesium anode generates enough hydrogen for those bacteria to produce hydrogen sulfide gas, which smells like rotten eggs[1].
That is why the smell often appears:
- After moving into a house on a private well.
- After a vacation, when hot water sat unused in the tank.
- Soon after a new water heater with a fresh magnesium anode is installed.
- When the water heater is set at a low temperature.
The fixes makers use
Bradford White's procedure has two parts[1]:
- Disinfect the tank. With the water and power or gas off, the tank is drained, the anode is removed, and 1/2 to 1 gallon of bleach is added through the hot outlet. The tank is refilled and left for at least 3 hours, and ideally a full day, then flushed until the chlorine smell is gone.
- Change the anode. The magnesium anode is replaced with a different anode the maker approves for odor problems (Bradford White names its own part).
Do not simply pull the anode out. It is the most common shortcut online and the worst one. Bradford White states that complete removal of the anode will void the warranty and shorten tank life[1]. Without it, the tank lining starts to corrode.
Who should do this? Removing an anode often takes a long breaker bar and enough force to twist a tank on its connections, and the tank must be drained and refilled correctly. Most homeowners have a licensed plumber do it. Ask for a replacement anode approved by your heater's maker, so the warranty stays intact.
Other approaches some plumbers use include powered anodes, which use a small electric current instead of a sacrificial metal, and treating well water before it reaches the heater. If the smell comes from your well, water treatment is the lasting fix.
Keeping it from coming back
- Use the hot water. Smell often returns after the heater sits unused. When you come back from a trip, run the hot taps for a few minutes.
- Keep the replacement anode. If a plumber installed a different anode for odor, make sure any future replacement uses the same approved type, not the original magnesium one[1].
- Fix the source if it is a well. If the cold water also smells, the heater will keep getting reinfected until the well water is treated.
- Never run the tank without an anode. It trades a smell problem for an early tank failure[1].
What it costs
HomeGuide's national range for anode rod replacement is $150 to $350, and $75 to $250 for flushing and cleaning a tank (August 2025)[2]. Chlorination is often quoted together with the anode change.
When to call a pro
- The smell returns after a flush, or appeared right after a new heater was installed.
- Anode replacement or tank chlorination: both mean draining and working on fittings.
- Both hot and cold water smell, and you are on a well (call a water treatment pro).
- Any rotten egg smell in the air near gas appliances: call the gas utility and 911 first.
More questions
Is rotten egg smelling hot water safe to bathe in?
Ask your water utility or a water testing lab if you are concerned. If the cold water also smells, or you are on a private well, have the water tested, because the source may be the supply rather than the heater.
Will turning up the temperature kill the bacteria?
Some plumbers raise the temperature temporarily as part of treatment, but it raises scald risk and often does not clear the problem alone. Chlorination plus an anode change is the approach Bradford White describes.
Sources
- Hydrogen sulfide odor (rotten egg smell) and chlorinating water heaters, Bradford White. Accessed 2026-10-06.
- Hot water heater repair cost (Aug 7, 2025), HomeGuide. Accessed 2026-10-06.
- What to do if you smell natural gas, CenterPoint Energy. Accessed 2026-10-06.
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