Water containing hydrogen sulfide gas (“H2S”) has a distinctive “rotten egg” odor, which may be especially noticeable when running hot water. If your water smells like sulfur or sewage, the real question is where it’s coming from, your well, your water heater, or your household plumbing, since the fix is different for each.
Such water can discolor coffee, tea, and other beverages and alter the appearance and taste of cooked foods. Hydrogen sulfide (“H2S”) gas is a nuisance that is not usually a health risk at concentrations typically found in household water.
Hydrogen sulfide can be toxic. Usually, the gas can be detected long before it reaches harmful concentrations. H2S is flammable and poisonous. While such concentrations are not typical, if gases are released in a confined area, they could cause nausea, illness, and, in extreme cases, death.
H2S dissolved in water can corrode plumbing metals such as iron, steel, copper, and brass, and exposed metal parts in washing machines and other water-using appliances. Switching to an aluminum rod in water heaters can help eliminate the odor while still providing corrosion protection.
The corrosion of iron and steel from hydrogen sulfide forms ferrous sulfide or “black water,” which can darken silverware and discolor copper and brass utensils. Hydrogen sulfide can also interfere with the effectiveness of water softeners and filter systems.
Run a hose bib or tap as close to the well as possible, fill a 5-gallon bucket or other container, and notice if there are odors. A “rotten egg” smell typically points to hydrogen sulfide gas.
Manganese usually shows up as black or brown staining and a metallic taste rather than a distinct odor. A scent resembling cucumbers or sewage is usually caused by iron or sulfur bacteria.
Run the hot water from each tap and notice if the odor only shows up in hot water, not cold. This indicates a problem with the water heater, not your well. Iron and sulfur bacteria can interact with the anode rod in water heaters, producing hydrogen sulfide gas only in hot water.
Changing the anode rod to an aluminum-zinc rod can often solve this problem.
It’s worth draining your water heater at least once a year. This flushes out sediment that accumulates in the bottom and gives you an idea of what type and how much is present.
If you’re experiencing a rotten egg odor, start by checking your water heater, it’s the most common culprit. If the odor is only present in hot water, the magnesium anode rod is likely reacting with naturally occurring sulfates to produce hydrogen sulfide gas.
Next, inspect your plumbing system, including pipes and fixtures, for signs of corrosion or mineral buildup. Also check your water softener, since it can sometimes contribute to the growth of sulfur-reducing bacteria. Working through these potential sources systematically helps you pinpoint the origin before you spend money on the wrong fix.
Add a cup of bleach to the pipes after installing a new softener or whole-house filter, and flush the water heater and household cold water pipes with some bleach to eliminate the odor.
Odors can still develop in the pipes because of biofilms, even when there’s no odor leaving the new treatment system itself. This tends to be worse in sections of plumbing that don’t get used much.
Introducing a small amount of chlorine (laundry bleach works fine) and letting the water sit for a couple of hours sanitizes the pipes and helps prevent odors from developing in them.
If the odor is primarily in hot water, the water heater needs sanitizing. Turn off the water pressure to the water heater, add 1 cup of chlorine bleach, and turn the water back on.
If you have a prefilter housing, add the bleach there. If not, remove the inlet flex pipe and drain some water out of the water heater. Run hot water in the home for a minute to mix the chlorine bleach in, then turn off the water. Let the water heater sit for 2 hours, then run the hot water until it’s clear. Severely fouled water heaters may need this repeated.
If the odor returns, you may need to remove or replace the anode rod entirely.
(Learn more about water odor.)
In some cases, the smell is worse on upper floors because the gas rises and shows up at fixtures higher in the house.
The fix is to shock chlorinate the household pipes: add enough bleach to reach a 100 to 200 ppm chlorine residual, then let the chlorinated water sit in the pipes overnight — 12 hours minimum. Note that this is a pipe flush, not a well shock; disinfecting the well itself uses a higher 200 ppm target and is covered in our shock chlorination guide.
Repeat the process if the odor disappears but returns within a few weeks.
An inline filter housing makes this easier to do repeatedly. With a spindown filter, you can turn off the water to the house, unscrew the filter, and add chlorine bleach or peroxide directly.
If you’ve ruled out your water heater and plumbing and the smell is coming from the well itself, whether it’s sulfur, sewage, or general “smelly water”, the cause is usually hydrogen sulfide gas, iron or sulfur bacteria, or occasionally septic contamination. For the full breakdown of causes and the actual fix (aeration, chlorination, ozone, or peroxide injection, and which filter media pairs with each), see our complete guide: Fix Well Water That Smells Bad.
Before choosing a treatment, it’s worth testing. Test your water for coliform bacteria using a lab kit or a do-it-yourself-at-home bacteria test kit, since a positive result changes the recommended fix.
The rotten-egg odor is usually caused by hydrogen sulfide gas (H₂S), which can come from sulfur bacteria, decaying organic matter, or chemical reactions in water heaters and plumbing systems.
H₂S is mostly a nuisance at low levels, affecting taste and smell. However, at high concentrations (rare in residential wells), it can be toxic, flammable, and corrosive to plumbing systems.
While it’s not usually dangerous at low levels, water with a sulfur odor should be tested to rule out high concentrations, bacteria, or other contaminants. It’s best not to drink it until it’s treated or tested.
Heating the water releases dissolved H₂S gas, which strengthens the odor. Magnesium rods in water heaters can also chemically create H₂S, intensifying the smell in hot water.
Run only cold water: if it smells, the source is likely your well water. If only the hot water smells, the water heater may be the issue. Replacing the anode rod or disinfecting the heater can help.
This usually means the gas is rising through the plumbing and showing up at higher fixtures first. Shock chlorinating the pipes (see above) typically resolves it.
See how we make clean water simple, with proven systems, easy installation, and a 90-day guarantee. Whether your well or city water smells off or leaves stubborn stains, you don’t have to face it alone. The same goes if it’s damaging your appliances.
Article last updated August, 2026 by Author.
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