Why Shower Water Smells Like Rotten Eggs
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Why shower water smells like rotten eggs usually comes down to hydrogen sulfide, a gas that can occur in some water supplies and that escapes from water more readily when the water is heated. The extension sources below describe a few common causes: sulfur-reducing bacteria in groundwater, the magnesium rod in an electric water heater, a water softener in some cases, and, rarely, sewage. Whether the smell shows up at the hot tap only or at both taps is the first clue, and the sources give simple checks to narrow it down.
Quick answer
- The smell is almost always hydrogen sulfide. Virginia Tech describes the gas as giving water a distinctive sulfur or rotten egg smell and taste, which may be especially noticeable in hot water.
- If the smell is only at the hot tap, the water heater is a likely source, and the UGA bulletin names it as a cause to check first.
- Low levels are described as a nuisance. Virginia Tech says the presence of low levels is not a health hazard, while the UGA bulletin says high levels in drinking water can cause nausea and stomach pain.
- If sewage is possible, test for bacteria and nitrate. Virginia Tech says that if sewage contamination is suspected, you should test your water for coliform bacteria and nitrate.
What hydrogen sulfide is and why shower water shows it
Hydrogen sulfide escapes from water easily. The UGA bulletin says that when water is pumped to the surface, the gas escapes and is easy to smell. Most people can detect hydrogen sulfide in water, according to Virginia Tech, and the UGA bulletin gives a threshold: most people can smell it in water with a concentration of as little as 0.5 parts per million (ppm).
The shower makes the smell stronger. The UGA bulletin says the odor may be noticeable only when the water is first turned on, or when hot water is running. Heat forces the gas into the air, and the bulletin says this “may cause the odor to be particularly offensive in the shower.” That is the reason the smell is often most noticeable during a shower and less so at a cold tap.
The Purdue bulletin, an older Indiana publication from 1990, makes the same point about temperature. It says that heated water releases hydrogen sulfide gas more quickly than cold water. The newer sources are more specific on the other questions, so this guide uses the Purdue bulletin only where it adds something on temperature, carbon and softeners.
What causes the smell
The UGA bulletin describes bacterial routes. Hydrogen sulfide can be produced by sulfur-reducing bacteria, and it can also form when sulfate-reducing bacteria reduce dissolved sulfate in low-oxygen environments. The bulletin adds that both sulfur- and sulfate-reducing bacteria are harmless to human health. That statement is about the bacteria themselves. The gas they produce is still a nuisance, and it can be corrosive.
Virginia Tech says that issues with sulfur-using bacteria that produce hydrogen sulfide gas may be controlled by disinfecting the water supply system using shock chlorination. That is a measure for the water system, usually a well system, and this guide does not cover how to carry it out.
The water heater is the second common cause. The UGA bulletin calls the magnesium corrosion control rod in many electric hot water heaters “another common source of hydrogen sulfide.” It explains that the rod can chemically convert naturally occurring sulfates in the water to hydrogen sulfide. The sentence that matters most for a shower is this one: if this is the sole source of hydrogen sulfide, only hot water will have this odor.
The UGA bulletin also lists an ion exchange water softener as another possible contributor to the odor. It does not say that every softener causes the problem, and it does not give a rate. Treat the softener as one possible cause to rule out, not as a confirmed one.
Sewage is the rare case. Virginia Tech says hydrogen sulfide gas in household water may also indicate sewage contamination, particularly in poorly constructed or shallow wells near leaky sewer lines or septic drainfields. The UGA bulletin says that in rare cases the odor may come from sewage pollution. Sewage can also bring coliform bacteria and nitrate into a supply, which is why that possibility is worth ruling out before assuming the smell is only a nuisance.
Hot water only or both?
The fastest check is to compare the hot and cold taps. The UGA bulletin says that if you detect the smell only from the hot water faucet, your water heater may be causing the problem. The fix it describes is to replace the magnesium rod with one made of aluminum or zinc, preferably by a licensed plumber. This guide does not cover water heater work, because that is a different job from a shower head change.
If cold water smells too, the water heater is not the sole source, by the UGA bulletin’s own logic. Virginia Tech points to the water supply, including sewage, and the UGA bulletin points to bacteria and sulfate in the water itself. Those are supply questions, and they are harder to solve at a single shower.
Write down what you notice before you call anyone. The useful details are whether the smell is strongest at the first run, whether it appears only with hot water, and whether it is also at the cold tap. A short list of observations helps a plumber, a utility, or a health department sort out the cause.
What to check at home
- Run the cold tap for a moment and smell the water at the first run. The UGA bulletin says the odor is often noticeable when the water is first turned on.
- Run the hot tap alone for a moment and compare. A smell only at the hot tap points at the water heater, according to the UGA bulletin.
- Check the shower again after the water has run for a while, and note whether the smell changes.
- Consider whether a recent change lines up with the smell. The sources name an ion exchange water softener as a possible contributor, but they do not give a timeline.
Home checks are a way to sort the cause, not a measurement. The UGA bulletin notes that on-site test kits exist for hydrogen sulfide, which is covered in the testing section below.
How strong is the smell?
The UGA bulletin gives three rough levels. The table below uses only what the bulletin states, and the cells say “not stated” where it is silent.
| Concentration | Smell described | Plumbing note |
|---|---|---|
| As little as 0.5 ppm | Most people can smell it | not stated |
| 0.5 to 1 ppm | Musty or swampy | not stated |
| Above 1 ppm | Rotten eggs | Corrosive to plumbing |
The table describes what people notice, not a result for your water. Your water may not match the bulletin’s rough levels, and the bulletin does not say whether the smell changes over time.
Health: what the sources say
Virginia Tech is direct on this point: the presence of low levels of hydrogen sulfide in household water is not a health hazard. It adds that hydrogen sulfide can make water more corrosive, which can leach metals from the plumbing. The same publication says that the offensive odor and other nuisance problems associated with hydrogen sulfide may make treatment desirable.
The UGA bulletin gives the other side. It says drinking water with high levels of hydrogen sulfide can cause nausea and stomach pain. It also says a harmful dose from drinking water is highly unlikely, because the taste and odor become unpleasant long before that point. The bulletin is describing drinking water, not bathing or showering.
The older Purdue bulletin says that hydrogen sulfide in water “causes no known health effects.” Its wording is broader than the newer sources, so this guide does not rely on it for health questions. The practical point is the same across sources: the smell is described as a nuisance at low levels, and a test is advised if sewage is possible.
Testing: what the sources say
A lab test is not always the best first step. The UGA bulletin says that “A laboratory test may be required to verify the level of hydrogen sulfide in” water. It also says the gas escapes very quickly, so by the time a sample reaches a lab the level may be lower than it was at the tap. The bulletin says the smell is unmistakable and that test kits are available for on-site measurement.
When sewage is possible, the test is different. Virginia Tech says to test for coliform bacteria and nitrate. Those results matter more than the smell, because they can point to a contamination problem rather than a nuisance. The Purdue bulletin says to contact the “Extension office or local Health Department” for help with questions about a supply.
For a private well, the UGA bulletin says that the presence of sulfate is easy to determine in laboratory water tests, and it advises choosing a test package that includes sulfate. That is a supply check, and it does not measure the odor at the shower.
What a shower filter can and cannot do here
The sources do not make a strong case for a shower filter. The Purdue bulletin says that activated carbon filters “absorb some hydrogen sulfide but have very limited” capacity “for major odor absorption.” That is the bulletin’s general statement about carbon, and the bulletin dates from 1990.
The NDSU extension page describes catalytic carbon in a different light. It says catalytic carbons “also may remove hydrogen sulfide gas” in some well water. That is a “may,” not a guarantee, and the page does not give a removal rate for a shower device.
The Purdue bulletin also says that ordinary household water softeners do not remove sulfur odors from water. That is one more reason a softener is not a fix for the smell, even though the UGA bulletin lists softeners as a possible contributor.
If you plan to change the head while you sort out the cause, the guides on water-efficient handheld shower heads and high-pressure shower heads that save water cover the flow side of that choice. Neither one addresses the gas, and the sources give no reason to expect a new head to change the odor.
When to call someone
Call a licensed plumber for water heater work, such as the magnesium rod. The UGA bulletin says the rod replacement is best done preferably by a licensed plumber. Call the utility or the local health department if the smell is in cold water as well as hot, or if sewage might be involved. The sources do not say who pays for any of these steps or who is responsible for the fix in a given home.
If you have a private well, the sources point to a test package that includes sulfate, and to a test for coliform bacteria and nitrate if sewage is possible. Those two checks answer different questions, so ask for both when sewage is in doubt.
How we chose
This explainer uses four sources, all opened on 2026-10-22. The criteria were extension publications from universities, with one NDSU extension page on activated carbon and catalytic carbon. The Purdue bulletin is older (1990), so each use from it is labelled as dated. Several other extension pages were left out: some returned server errors, and a University of Maryland page opened with navigation text and no bulletin content. The post does not rank products or recommend a model.
What we could not verify: what the sources do not say
- The sources do not say how common the smell is in any region outside the Indiana bulletin’s area.
- No source gives a removal rate for a shower-level device or for catalytic carbon in a shower.
- The sources do not give a replacement interval for the water heater magnesium rod.
- The sources do not say how long the smell lasts after the water has run.
- The sources do not say who is responsible for the fix in a given home.
- No source opened here gives a health threshold for showering in water with hydrogen sulfide.
- The sources do not say how a softener contributes in a given home.
Frequently asked questions
Is rotten egg smell in shower water dangerous?
Virginia Tech says low levels of hydrogen sulfide are not a health hazard and are mainly a nuisance that can corrode plumbing. The UGA bulletin says high levels in drinking water can cause nausea and stomach pain. If sewage is possible, test for coliform bacteria and nitrate, because those results matter more than the smell.
Why does the smell show up only when the water is hot?
Heat releases the gas faster, according to the Purdue bulletin. The UGA bulletin also says a water heater with a magnesium rod can produce hydrogen sulfide, and that if the heater is the only source, only hot water will smell.
Will a shower filter remove the smell?
The sources do not give a shower-level result. The Purdue bulletin says carbon absorbs some hydrogen sulfide but has very limited capacity. The NDSU page says catalytic carbon may remove it in some well water. Neither gives a removal rate for a shower product.
Will a new shower head fix it?
The sources place the cause in the water supply, the water heater, a softener or sewage, not in the shower head. None of them says a new head changes the odor.
How do I check whether the smell is from the water heater?
Compare the hot and cold taps. If the smell is only at the hot tap, the UGA bulletin says the water heater may be causing it. A licensed plumber is the right person to examine the rod.
Who should I contact if the smell is in cold water too?
The Purdue bulletin points to the extension office or local health department. For a private well, the UGA bulletin recommends a test package that includes sulfate, and Virginia Tech says to test for coliform bacteria and nitrate if sewage is possible.
Bottom line
If the smell is only at the hot tap, check the water heater first. If it is at both taps, test the water supply before you buy a filter or a new head.
Sources
- Virginia Tech Extension, Publication 442-658, “Sulfate and Hydrogen Sulfide in Household Water,” https://ext.vt.edu/content/pubs_ext_vt_edu/en/442/442-658/442-658.html (opened 2026-10-22)
- University of Georgia Extension, “Hydrogen Sulfide and Sulfate,” household water quality series, circular 858-8, https://aesl.ces.uga.edu/publications/watercirc/HydrogenSulfide.pdf (opened 2026-10-22)
- Purdue Extension, WQ-11, “Sulfur Water Control (Rotten Egg Odor in Home Water Supplies),” dated 1990, https://www.extension.purdue.edu/extmedia/wq/wq-11.html (opened 2026-10-22)
- North Dakota State University Extension, “Filtration: Sediment, Activated Carbon, and Mixed Media,” https://www.ndsu.edu/agriculture/extension/publications/filtration-sediment-activated-carbon-and-mixed-media (opened 2026-10-22)
