Why Does My House Smell Like Rotten Eggs? Gas, Sewer or Water
Three very different problems share one smell. One of them is an emergency. The other two are plumbing fixes you can often handle with a bucket of water or a call to a plumber.
Quick answer
If you have gas service and the smell is in the air, especially near the stove, furnace, water heater or meter, treat it as a leak: leave without touching switches or phones, then call the gas company or 911 from outside. A smell from a floor drain or unused sink or shower means a dry trap is letting sewer gas in. If only the hot water smells, the water heater is making hydrogen sulfide.
- Difficulty
- Easy DIY
- Smell in the air, gas home
- Possible gas leak: leave, then call
- Smell from a drain
- Dry trap. Pour water into it
- Only the hot water smells
- Water heater anode or bacteria
- Never
- Flip switches or use a phone near a gas smell
On this page
The rotten-egg smell comes from sulfur compounds. In a gas leak, it is the odorant utilities add on purpose so you can notice the gas. In sewer gas and smelly water, it is hydrogen sulfide made by bacteria and chemical reactions. Where the smell is strongest, and when it appears, tells you which.
If you have natural gas or propane and the smell is in the air, assume it is gas. Leave the building and tell everyone else to leave. Do not flip light switches, use a phone or the doorbell, adjust the thermostat or light a match. Call the gas company or 911 from outside or a neighbor’s home, and do not go back in until they say it is safe. Utilities check gas leaks at no charge.
Which smell is it?
| Clue | Likely source | What to do |
|---|---|---|
| Smell in the air near the stove, furnace, water heater, dryer or meter | Natural gas or propane leak | Leave, then call the gas company or 911 |
| Hissing sound near a gas line or meter | Gas leak | Leave, keep people away, call from a distance |
| Strongest at one floor drain, basement drain, or an unused sink, tub or shower | Dry drain trap letting sewer gas in | Run water into every drain |
| Around the base of a toilet | Failed wax seal | Plumber, or reset the toilet with a new seal |
| Whole house, worse upstairs or after rain, drains slow | Blocked plumbing vent or sewer line | Plumber |
| Only from hot water taps | Water heater making hydrogen sulfide | Plumber: disinfect tank or change anode |
| Hot and cold water both smell (well water) | Hydrogen sulfide in the groundwater or well | Test water; treatment or well disinfection |
| Near the sump pit or a sewage ejector | Unsealed or dry pit, or sewage | Seal the lid; plumber |
If it is the drains: refill the traps
Every sink, tub, shower and floor drain has a trap, a U-shaped bend that holds a plug of water. That water is the only barrier between your house and the sewer gas in the drain line. In a guest bathroom, a basement floor drain or a seldom-used laundry sink, it can evaporate, especially in dry winter air.
- Run water into every drain for 20 to 30 seconds.
Include floor drains (pour in a bucket), the basement laundry sink and showers nobody uses.
- Flush toilets that sit unused.
A toilet’s trap is built into the bowl and can dry out the same way.
- Wait an hour and sniff again.
If the smell is gone, it was a dry trap. For drains that keep drying out, add water on a schedule or ask a plumber about a trap primer or seal.
- If it persists, call a plumber.
A failed toilet wax ring, a cracked drain pipe, a blocked roof vent or a sewer line problem can all let gas in. Oatey lists these as the main causes after dry traps.
If it is only the hot water
The Minnesota Department of Health explains that a water heater can be an ideal place to turn sulfate in the water into hydrogen sulfide. The tank is warm enough for sulfur bacteria, and the magnesium anode rod that protects the tank from corrosion can drive the same reaction. The smell shows up mainly in hot water, and often after the heater has sat unused, such as after a vacation.
Fixes a plumber may suggest:
- Disinfect and flush the tank with a chlorine solution to kill the bacteria.
- Replace the magnesium anode with a different type (often aluminum or zinc-aluminum). Removing the anode entirely stops the smell but shortens the tank’s life and can void its warranty, as MDH and Penn State Extension note.
- Heat the tank temporarily to kill bacteria, a method both agencies describe. It carries a real scalding risk and should follow the manufacturer’s instructions and a working relief valve, then be turned back down.
If you are on a private well and cold water smells too, the gas is likely in the well or groundwater. MDH recommends testing for coliform bacteria and nitrate to be safe, then choosing treatment based on the level.
Smell plus a water heater that pops or rumbles? Sediment and sulfur problems often travel together. See why a water heater pops and how long water heaters last.
Other sources
- A dead animal in a wall, crawl space or attic produces a sulfurous, rotten smell that grows over days. A pest-control company can find and remove it.
- Electrical overheating smells more like burning plastic or fish than eggs, but if any odor comes from an outlet, switch or the panel, turn that circuit off if safe and call an electrician.
- A gas appliance with a pilot out can leak a small amount of gas. Connecticut’s utility regulator notes that a pilot light that has gone out or a burner valve left slightly open can cause a faint smell near an appliance. If you are unsure or the smell is strong, leave and call.
Frequently asked questions
Does natural gas smell like rotten eggs?
Natural gas has no smell of its own. Gas companies add an odorant called mercaptan to give it the rotten-egg smell, so a leak can be noticed. Propane is odorized too.
What should I do if I smell gas in my house?
If the smell is strong, or you are unsure, leave right away and tell others to leave. Do not switch lights on or off, use the phone, ring the doorbell, adjust the thermostat or light anything. Call the gas company or 911 from outside or a neighbor’s home, and stay out until they say it is safe. Gas companies respond to leaks around the clock at no charge.
Why does my bathroom smell like rotten eggs?
Most often a drain trap has dried out, letting sewer gas past. Run water in every sink, tub and shower, flush the toilet, and pour water into floor drains. If the smell continues, the toilet wax seal or a plumbing vent may have failed, which a plumber can check.
Why does only my hot water smell like rotten eggs?
When the smell is only in the hot water, the water heater is usually the source. The Minnesota Department of Health explains that the magnesium anode rod and sulfur bacteria in the warm tank can convert sulfate in the water into hydrogen sulfide gas. A plumber can disinfect the tank or swap the anode for a different type.
Is a rotten egg smell from the drain dangerous?
At the low levels that escape from a dry trap, hydrogen sulfide is mainly a nuisance, but the gap it comes through also lets other sewer gases in, and high concentrations are harmful. Fix the source rather than masking it, and ventilate the room.
Sources
- What To Do If You Smell Natural Gas Connecticut Public Utilities Regulatory Authority
- Why Does My Water Smell Like Rotten Eggs? Hydrogen Sulfide and Sulfur Bacteria in Well Water Minnesota Department of Health
- Hydrogen Sulfide (Rotten Egg Odor) in Water Wells Penn State Extension
- Why Does My House Smell Like Sewer Gas? (And How to Fix It) Oatey
First published October 7, 2026. Last reviewed October 7, 2026. Spot an error? Tell us and we will check it against the source.