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That Rotten-Egg Smell: Sulfur Water or a Gas Leak?
When water smells like rotten eggs, it is usually hydrogen sulfide from the aquifer or the water heater. But natural gas is scented to smell the same, so if the smell is anywhere but the running tap, leave first.
Sulfur water is part of life on Floridan groundwater. Florida's health department says hydrogen sulfide can occur in wells anywhere in Florida, and every city plant here has a step meant to strip it out. The trouble is that the same smell is used on purpose as a warning for natural gas, so the first job is to be sure which one you have.
Is it the water, or is it gas?
If you smell rotten eggs anywhere other than right at a running faucet, treat it as gas and get everyone out of the house. Natural gas has no smell of its own; Peoples Gas adds an odorant that smells like rotten eggs so people notice a leak. Peoples Gas says to leave immediately, not to look for or stop the leak, and not to do anything that might make a spark: no light switches, no phones or battery devices, no garage door opener, no starting a car nearby. Once outside and well away, call 911, then the gas company.
Sulfur water behaves differently: the smell comes with running water, is strongest at the sink or shower, and fades once the tap is off. A smell in a closed room, near the stove, gas water heater, dryer or meter, or out in the yard is not a water problem until proven otherwise. Peoples Gas also warns not to rely on your nose alone, since a steady whiff dulls the sense of smell and other odors can cover gas; a hissing sound or dirt blowing near a line are other signs.
Where does the sulfur smell come from?
Usually from the aquifer itself. Sanford's FAQ says raw groundwater here naturally contains gases like hydrogen sulfide, and the utilities remove it before the water reaches you: ozone at OUC and Sanford's Plant No. 2, aeration at Sanford's Plant No. 1 (with an upgrade under way) and at Altamonte Springs, Longwood, Winter Springs and Oviedo. Inside the house, the culprits are the water heater, sulfur bacteria in a well or the plumbing, and now and then a softener. Sanford adds that a foul smell when you first open the faucet is often bacteria living on soap and food scraps in the drain trap, not the water at all.
Hot tap only, or hot and cold?
Florida DOH's odor and staining sheet gives a simple test: fill a glass from the cold tap, then from the hot, and smell each away from the sink. Heat makes the gas come out of the water, so the hot side often smells stronger either way.
What the hot-or-cold test points to (Florida DOH)
| What you notice | Likely source |
|---|---|
| Smell only from the hot faucet | The water heater |
| Hot and cold, but only on softened water | Sulfur bacteria in the softener |
| Strong at first in hot and cold, fading as it runs | Sulfur bacteria in the well or plumbing |
| Strong and steady in hot and cold | Hydrogen sulfide in the groundwater |
On city or county water, a strong, steady smell from both taps is worth a call to the utility, since its plant is supposed to remove the sulfide. On a well, it usually means the aquifer at your well carries sulfide.
Is rotten-egg water harmful to drink?
In the amounts that reach a kitchen tap, it is mainly a nuisance. Penn State Extension calls hydrogen sulfide in drinking water an aesthetic problem and notes that most people can smell it well below 0.5 mg/L, long before it reaches a level that causes health concerns. Higher levels corrode metal and leave yellow or black stains. Florida DOH says sulfur bacteria are not harmful and the smell usually tells you nothing about whether a well is clean, so well owners still need the yearly bacteria test described in our private wells story.
What fixes a smelly water heater?
When only the hot side smells, the heater is the usual source: its anode rod or bacteria growing in the tank. Penn State explains that a magnesium anode can turn sulfates into hydrogen sulfide and suggests swapping it for an aluminum one; A. O. Smith suggests a special zinc anode in some cases and calls chlorination the only sure cure for the bacteria. Any replacement anode should be the type your heater's maker specifies. Never pull the anode out and leave it out: Penn State warns that shortens the heater's life and will likely void the warranty.
Temperature matters too. Sanford notes bacteria can multiply in heaters set below 120°F, and 120°F is also the setting the Consumer Product Safety Commission urges to prevent scalds. Homeowners can shut off the water and the breaker and drain per the manual; gas burners, gas valves and wiring are jobs for a licensed pro. See our water heaters story for more.
What treats sulfur in well water?
It depends on how much sulfide the water carries, so test before buying anything. Penn State gives rough working ranges: activated carbon for small amounts, below about 1.0 mg/L; aeration, normally not used above about 2 mg/L; an oxidizing filter such as manganese greensand, up to 2 to 3 mg/L; and continuous chlorination with filtration, which handles any level and is most often used above 6.0 mg/L. Catalytic carbon only works when the water holds 4.0 mg/L or more of dissolved oxygen.
mg/L of hydrogen sulfide; chlorination row shows where it is most often used, Penn State Extension
Source: Penn State Extension
A lab report that helps you choose should show the hydrogen sulfide level, iron, manganese and dissolved oxygen, plus a bacteria result. Shock-chlorinating the well is often only a short fix, since Penn State says the odor tends to come back quickly. Our whole-house filters story covers carbon filters.
Readers often ask
Why does only my hot water smell like rotten eggs?
The water heater is the likely source, through its anode rod or bacteria in the tank; DOH's tap test points there when the cold side smells clean.
My whole house smells like sulfur, not just the sink. What now?
Treat it as a possible gas leak. Get everyone outside without touching switches or phones, then call 911 and your gas company from a safe distance.
Can I shower in water that smells like sulfur?
At the low levels that reach most taps, Penn State calls hydrogen sulfide a nuisance rather than a health concern, and DOH says sulfur bacteria are not harmful. Well owners should still test yearly for bacteria.
Will a water softener get rid of the smell?
A softener is built to remove hardness, not sulfide, and DOH and Penn State both note that a softener can occasionally be where sulfur bacteria grow. Match treatment to a tested sulfide level.
Why did the smell come back after I shocked my well?
Penn State says sulfur-reducing bacteria and the odor usually return quickly after shock chlorination. Choose a lasting fix from a lab result showing the sulfide level.
Where this came from
- Peoples Gas — If You Smell Gas — odorant, leave-first steps, other warning signs
- Peoples Gas — Counties and communities served (tariff) — local towns on the service list
- Florida DOH — Well Water Facts: Odor & Staining — causes and the hot-or-cold test
- Penn State Extension — Hydrogen Sulfide (Rotten Egg Odor) in Water Wells — detection level, anode, treatment ranges
- A. O. Smith — Electric water heater manual — bacteria in heaters, zinc anode, chlorination
- City of Sanford — Drinking Water FAQ — plant treatment, 120°F, drain-trap odor
- Orlando Utilities Commission — Water quality reports — ozone treatment
- CPSC — Avoiding Tap Water Scalds — 120°F setting