A rotten-egg smell from your tap is hard to ignore, especially when it shows up in a glass of water or a hot shower. The odor is often linked to hydrogen sulfide, a gas that can occur naturally in water or form inside plumbing. But the smell can also come from your drain or water heater, so the quickest fix depends on where and when you notice it.
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Why tap water can smell like rotten eggs
The most common cause is hydrogen sulfide, a colorless gas with a strong sulfur-like odor. Some people can smell it at very low levels, which is why a noticeable smell doesn’t automatically mean there’s a large amount in your water or that the water is unsafe.
Hydrogen sulfide can get into water in a few ways. It may occur naturally in groundwater, especially where water moves through certain underground rock or soil. It can also be produced by sulfur bacteria in wells, plumbing, or a water heater. These bacteria use sulfur compounds in their surroundings and create hydrogen sulfide as a by-product.
Other sulfur compounds can cause similar odors, and sometimes the smell isn’t coming from the water at all. A drain, dirty faucet aerator, or water-heater reaction can make it seem as if the tap itself is the problem.
How to track down the source
Before buying a filter or calling a plumber, check where the smell happens. A few simple comparisons can narrow things down and help you explain the issue if you need professional help.
Compare hot and cold water
Run the cold tap into a clean glass, then run the hot tap into a different clean glass. Take both away from the sink before smelling them. If only the hot water has the odor, the water heater is a strong suspect. If both smell, the cause may be in the incoming water, well, or plumbing shared by both supplies.
A hot-water-only odor often happens because sulfate in the water reacts with the heater’s anode rod. The rod is designed to protect the tank from corrosion. In some conditions, its reaction can encourage hydrogen sulfide to form. Sulfur bacteria inside the heater can also contribute.
Check more than one tap
Try a bathroom faucet and a kitchen faucet, ideally on both hot and cold settings. If just one tap smells, the cause may be local: a dirty aerator, a faucet component, or a nearby section of plumbing. If several taps have the same odor, the source is more likely to be shared—such as the water supply, well, or water heater.
See whether the smell is really from the drain
Run water into a clean glass, step away from the sink, and smell the glass. If the water smells normal but the odor is strongest beside the drain, the drain may be the culprit. Buildup inside a drain or a dry trap can let unpleasant sewer-like odors escape into the room.
A faucet aerator can also collect sediment and organic material. Unscrew it only if you’re comfortable doing so, rinse it, and clean it according to the faucet maker’s instructions. If the smell remains, don’t assume the aerator was the whole problem.
| What you notice | Possible source | Useful next step |
|---|---|---|
| Only hot water smells | Water heater, anode rod, or bacteria in the tank | Ask a plumber or water-treatment professional to inspect the heater |
| Hot and cold water smell at several taps | Incoming water, well, or shared plumbing | Contact your water provider or arrange appropriate water testing |
| One faucet smells, but others do not | Aerator or local plumbing | Clean the aerator and compare the water in a clean glass |
| The smell is near the sink, but water in a glass seems normal | Drain or trap odor | Check the drain and seek plumbing help if it continues |
Common causes in more detail
Hydrogen sulfide in groundwater
Private wells draw water from underground, where natural minerals and low-oxygen conditions can allow hydrogen sulfide to occur. The smell may be present in cold water from multiple taps, and it can vary as groundwater conditions change.
Well owners should not rely on smell alone to judge water quality. A laboratory test can check for hydrogen sulfide and other concerns, including bacteria and minerals. Use a lab or testing service recommended by your local health department, and follow its instructions for collecting a sample. A sample taken incorrectly may not give a useful result.
Sulfur bacteria in a well or plumbing
Sulfur bacteria can live in a well, water-treatment equipment, or plumbing. They may create hydrogen sulfide and sometimes form a slime or film. Finding these bacteria doesn’t automatically mean disease-causing bacteria are present, but it’s a good reason to get the water checked rather than treating the odor as only a nuisance.
Disinfecting a well may be appropriate in some cases, but the right method depends on the well and the test results. Pouring chemicals into a well without guidance can damage equipment or fail to solve the problem. Ask your local health department or a qualified well contractor what to do.
A reaction inside the water heater
If the odor appears only in hot water, focus on the heater. The tank’s anode rod helps prevent corrosion, but certain combinations of water chemistry and rod material can produce a sulfur smell. Bacteria inside the tank are another possibility.
A plumber can inspect the heater and recommend a safe fix. Depending on the cause and the heater, that might involve cleaning or disinfection, adjusting the anode rod, or replacing a part. Don’t remove the anode rod yourself as a quick fix: doing so can leave the tank more vulnerable to corrosion and may affect the warranty. Water heaters also contain very hot water and can be dangerous to work on.
Municipal water or building plumbing
If you’re connected to a public water system and the smell affects several taps, contact your water provider. The odor could be related to source water, treatment, or plumbing in your home or building. Your provider can tell you whether other customers have reported a similar issue and whether it recommends testing or another step.
In an apartment or shared building, ask the property manager whether nearby units have the same problem. A smell limited to your unit may point toward local plumbing; a smell across several units may suggest a shared system.
What to do about the smell
Start with the observations above, then match the next step to the likely cause. A filter is not a one-size-fits-all solution: a product that helps with one water problem may do little for another. If you don’t know what’s in the water, test first and choose treatment based on the results.
- If only hot water smells: Have the water heater checked by a qualified plumber. Avoid opening or modifying the heater yourself.
- If you have a private well: Arrange testing through a qualified lab or local health department. Ask whether the well and treatment system need inspection.
- If you use municipal water: Contact your water provider, especially if the odor appeared suddenly or affects more than one home.
- If the smell seems to come from one drain: Clean the drain and check that the trap has water in it. Call a plumber if the odor persists or returns.
- If you’re considering treatment: Compare options only after you know the cause. A water-treatment professional should explain what the system removes, how it’s maintained, and what testing supports the recommendation.
Treatment for confirmed hydrogen sulfide may involve methods such as aeration, oxidation, or filtration. Which one is suitable depends on the water chemistry and the amount of the problem. For example, a system designed to remove sulfur odors may need different maintenance from a basic carbon filter. Ask for the treatment recommendation in writing and make sure the equipment is appropriate for your test results.
Is rotten-egg-smelling water dangerous?
The odor alone can’t tell you whether water is safe to drink. Hydrogen sulfide at levels that create a smell in household water is often mainly a taste and odor problem, but that doesn’t rule out other water-quality issues. A private well, in particular, can have contaminants that have no smell or visible signs.
If the smell starts suddenly, is unusually strong, or comes with a change in color or appearance, stop using the water for drinking and cooking until you’ve contacted your water provider or local health department for advice. If anyone becomes ill after drinking it, seek medical advice and report the issue. Don’t try to make water safe simply by boiling it; boiling does not address every possible contaminant.
If you’re on a public supply, follow any notice or instructions from your water provider. If you’re on a well, get the water tested rather than assuming it’s safe because the smell goes away.
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Frequently Asked Questions
Why does my tap water smell like rotten eggs only in the morning?
Water sitting in pipes overnight can make an existing odor more noticeable in the first glass. A buildup in the faucet aerator or a nearby plumbing issue may also contribute. Compare water from several taps and check whether the smell fades after running it briefly; if it keeps happening, contact your water provider or arrange testing.
Why does only my hot water smell like sulfur?
A hot-water-only smell often points to the water heater. Sulfate in the water may react with the anode rod, or bacteria may be present in the tank. Have a plumber inspect it rather than removing parts yourself.
Will a water filter remove the rotten-egg smell?
Some treatment systems can reduce hydrogen sulfide, but the right option depends on the water and the cause. A basic filter may not solve the problem. Test the water or ask your provider about it before choosing equipment.
Should I drink water that smells like rotten eggs?
Smell by itself can’t confirm whether water is safe or unsafe. If the odor is new, strong, or accompanied by other changes, use another known-safe source for drinking and cooking while you contact your water provider or local health department.
Conclusion
A rotten-egg smell usually points to hydrogen sulfide, sulfur bacteria, a water-heater reaction, or an odor coming from the drain rather than the water itself. Compare hot and cold water, check more than one tap, and smell water in a clean glass away from the sink to narrow down the source.
Once you have a likely cause, get the right help: a plumber for a hot-water issue, your water provider for a public-supply concern, or a qualified lab or health department for a private well. Testing first makes it much easier to choose a fix that actually works.
