Only hot water smells like rotten eggs
Cold water smells normal, but showers and hot taps have a sulfur odor.
Start here: Check multiple fixtures and confirm the smell appears only on the hot side before working on the heater.
Hot water odor troubleshooting
Water Heater Smells Like Sulfur
Direct answer: A sulfur or rotten-egg smell tied to the water heater is usually caused by bacteria reacting inside the tank or by a worn water heater anode rod, not by a failed heating element or burner.
Most likely: If the smell is strongest in hot water and especially after the water sat overnight, start with the tank itself: flush some water, compare hot versus cold at more than one faucet, and pay attention to whether the odor fades after a minute of flow.
First separate hot-only odor from odor in both hot and cold water. That one check saves a lot of wasted work. Reality check: a nasty sulfur smell often comes from a tank that still heats fine. Common wrong move: dumping random chemicals into the tank without confirming the source.
Don’t start with: Do not start by replacing heating parts, gas parts, or the whole water heater just because the smell is bad.
If only hot water smellsFocus on the tank, anode rod, and bacteria inside the water heater first.
If hot and cold both smellThe source is likely in the incoming water or plumbing, not the water heater alone.
Last reviewed: 2026-04-04
What the sulfur smell is telling you
Hot and cold water both smell
The odor is present no matter which temperature you use.
Start here: This points away from the water heater and toward the incoming water or house plumbing.
Smell is worst after water sits
First draw in the morning smells strong, then improves after running for a minute or two.
Start here: Stagnant water and tank bacteria are more likely than a failed component.
One faucet smells worse than the rest
A bathroom sink or guest bath smells bad, but other fixtures are much better.
Start here: Check that fixture and its branch piping before blaming the whole water heater.
Most likely causes
1. Bacteria reacting inside the water heater tank
This is the most common reason for hot-water sulfur odor, especially after low use, vacation, or warm stagnant water sitting in the tank.
Quick check: Run hot water at two different fixtures for a minute. If the smell is strongest at first and then eases, tank bacteria is a strong suspect.
2. Worn or reactive water heater anode rod
The anode rod can react with certain water conditions and create a rotten-egg smell even when the heater still works normally.
Quick check: If the smell is hot-water-only, keeps returning after flushing, and the tank is otherwise heating fine, the anode rod moves up the list.
3. Odor coming from the water supply, not the heater
If both hot and cold smell, the water heater is usually not the root cause.
Quick check: Fill one glass with cold water and one with hot water from the same faucet, then compare. Repeat at a second fixture.
4. Localized odor at one fixture or branch line
A sink drain, faucet aerator, or little-used branch can make it seem like the water heater is the problem when it is not.
Quick check: Test the smell at the kitchen sink, a bathroom sink, and the tub or shower. If only one spot is bad, stay local first.
Step-by-step fix
Step 1: Confirm whether the smell is hot-only or everywhere
This is the fastest way to separate a water heater problem from a water supply or fixture problem.
- At one faucet, run cold water into a clean glass and smell it right away.
- Run hot water into a second clean glass from the same faucet and compare.
- Repeat at a second fixture on another side of the house if possible.
- Note whether the smell is only on hot, on both hot and cold, or only at one fixture.
Next move: If the smell is only in hot water at multiple fixtures, keep going with tank-focused checks. If both hot and cold smell, or only one fixture smells, the water heater is probably not the main problem.
What to conclude: Hot-only odor points to the water heater tank or anode rod. Hot-and-cold odor points upstream. One-fixture odor points local.
Stop if:
- You smell gas near the water heater.
- Water is leaking from the tank, fittings, or relief valve area.
- The odor is accompanied by discolored water, heavy sediment, or signs of contamination you cannot identify.
Step 2: Flush stale hot water and see whether the odor fades
A smell that is strongest after sitting often comes from stagnant hot water and bacterial activity, not a failed heating part.
- Pick the fixture closest to the water heater and run hot water for 2 to 3 minutes.
- Then test a farther fixture and see whether the odor is weaker than it was at first draw.
- If the heater has been lightly used, run enough hot water to bring in fresh water to the tank, but do not empty the tank through fixtures.
- Pay attention to whether the smell fades quickly, stays constant, or gets stronger as more hot water is used.
Next move: If the smell fades after fresh hot water moves through, the tank likely needs cleaning or service rather than random part replacement. If the smell stays strong every time hot water is used, the anode rod or persistent tank contamination becomes more likely.
What to conclude: A fading odor usually means stale water conditions. A steady recurring odor points to an ongoing reaction inside the heater.
Step 3: Check for a one-fixture false alarm before opening the heater
A smelly drain or dirty aerator can fool you into chasing the water heater when the problem is right at the sink.
- If one sink smells much worse than the rest, remove and rinse the faucet aerator if accessible.
- Run water directly from the spout without the aerator and compare the smell.
- Smell the drain opening separately from the water stream; drain odor often gets mistaken for water odor.
- If a guest bath or little-used faucet is the only bad one, run that fixture for a few minutes on both hot and cold and retest later.
Next move: If the smell is isolated to one fixture and improves after cleaning or flushing that fixture, leave the water heater alone. If multiple hot fixtures still smell the same, go back to the heater as the source.
Step 4: If the smell is hot-only and keeps returning, inspect the water heater service path
At this point the two most likely heater-side causes are tank bacteria and an anode rod reaction.
- For an electric water heater, turn off power at the breaker before removing any access panels or touching service parts.
- For a gas water heater, do not disassemble burner, gas valve, or vent parts for this odor issue.
- Look for basic service clues: age of the heater, heavy sediment at the drain, signs it has sat unused, and whether the drain valve will pass water cleanly into a hose or bucket.
- If the tank has never been flushed or has obvious sediment, a controlled tank flush is the first corrective move.
- If the tank has been flushed and the sulfur smell keeps coming back in hot water only, the water heater anode rod is a supported next suspect.
Next move: If flushing reduces the odor for a meaningful stretch, sediment and bacteria were likely driving the smell. If flushing helps little or the smell returns quickly, the anode rod is more likely involved.
Step 5: Take the next action that matches what you found
The right finish depends on whether the smell is supply-related, local to one fixture, or confirmed to be coming from the water heater.
- If both hot and cold water smell, stop working on the heater and investigate the incoming water source or call your water utility or a plumber.
- If only one fixture smells, clean that fixture, flush the branch, and monitor before doing heater work.
- If hot water at multiple fixtures smells, start with a proper water heater flush.
- If the heater is electric, hot-water-only odor keeps returning after flushing, and the tank is otherwise sound, replacing the water heater anode rod is the most supported parts path on this page.
- If the tank is leaking, badly corroded, or you are dealing with a gas unit and are not set up for safe service, schedule a pro instead of forcing a repair.
A good result: If the odor is gone after flushing or anode-rod service, verify at several fixtures over the next day or two.
If not: If the smell persists after the right corrective step, you are likely into water-quality treatment or professional diagnosis rather than another random water-heater part.
What to conclude: A sulfur smell is usually fixable, but only after you pin down where it starts.
Replacement Parts
Repair Riot may earn a commission from qualifying purchases, at no extra cost to you.
FAQ
Why does my hot water smell like rotten eggs but cold water does not?
That usually points to the water heater, not the house supply. The most common causes are bacteria inside the tank or a water heater anode rod reacting with your water.
Can a bad heating element cause sulfur smell in an electric water heater?
Usually no. A failed water heater heating element causes no-hot-water or slow-recovery problems, not a rotten-egg odor. Sulfur smell is much more often tied to tank conditions or the anode rod.
Will flushing the water heater fix the smell?
Sometimes, yes. If the odor is tied to stagnant water or sediment, a proper flush can reduce or remove it. If the smell returns quickly, the water heater anode rod or a broader water-quality issue is more likely.
Should I replace the whole water heater because it smells bad?
Not as a first move. Many sulfur-smell complaints come from serviceable issues like sediment, bacteria, or an anode rod reaction. Replace the whole unit only if the tank is leaking, badly corroded, or otherwise at the end of its life.
What if every faucet smells, even on cold water?
Then the water heater is probably not the main source. Check the incoming water supply, well system if you have one, or local plumbing conditions before replacing water heater parts.
Is sulfur smell from hot water dangerous?
The smell itself is usually more of a water-quality and nuisance issue than an immediate appliance failure. The bigger safety concerns are gas odor, tank leaks, scalding water, or unsafe service work around electrical and gas components.