Sewer Smell in House? Causes and What to Do
Short answerA sewer smell in the house? First check for a dry drain trap, which you can fix by running water into unused drains. If the smell stays, the cause may be a bad toilet seal, a vent problem or a damaged sewer line, which a plumber should find. If it could be gas, leave the house first.
Safety first
- Natural gas also smells like rotten eggs. If you are not sure which smell it is, or you hear hissing, leave the house and call 911 or the gas company from outside.
- Do not rely on your nose. People can stop noticing sewer gas after 2 to 15 minutes at high levels. Leave if you feel dizzy or sick, or the smell is strong, and get fresh air.
- Avoid touching sewage. Cleanup after a backup matters for your health. If sewage is backing up, stop using water and call a plumber.
Likely causes
| Cause | How to tell | What fixes it |
|---|---|---|
| Dry drain trap | The smell is near a drain you rarely use, such as a guest bath, floor drain or basement sink. | Pour about a quart of water into the drain, and repeat weekly or monthly. |
| Failed toilet seal | The smell is around the toilet base, sometimes with water on the floor. | See our guide on a toilet leaking at the base, or have a plumber replace the seal. |
| Blocked or damaged vent or drain pipe | The smell comes and goes, and drains gurgle or run slowly. | A plumber traces and repairs the pipe. |
| Blocked sewer or failing septic system | Several drains are slow, toilets back up, or there is soggy ground over a drainfield. | A plumber or septic pro inspects it, often with a camera. |
Why this is a job for a professional
- The smell stays after you pour water into every unused drain.
- Toilets or drains back up, or you see sewage.
- Ask: did you use a camera or smoke test to find the source? Is the problem on my side or the utility's? Do I need a backflow valve? Can I see the footage and a written price before work starts?
What it costs to have fixed
Sewer Line Repair is estimated at $1,100 to $5,800 nationally. See your state
Common questions
Why does my bathroom smell like sewage?
Check for a dry trap first, including the shower and floor drains. Then look at the toilet base. Water in a trap blocks gas from the sewer line, and a trap that has dried out lets it in.
Is sewer gas dangerous?
It can be. Sewer gas contains hydrogen sulfide, which is flammable, and strong exposure affects breathing and the nervous system. Get to fresh air if the smell is strong or you feel sick.
Why do I smell sewage when it rains?
Heavy rain can overload a sewer or saturate the soil around a septic system, causing backups. Cut back on water use, and call a plumber if it keeps happening. A backflow valve may help but needs maintenance.
Can you always smell sewer gas?
No, so do not rely on your nose. ATSDR says people can smell hydrogen sulfide, often called sewer gas, at very low levels, but lose the ability to smell it after about 2 to 15 minutes at about 100 ppm. If a strong smell fades or you feel sick, we recommend getting to fresh air and calling a plumber, and if it could be a gas leak, leave first. Source
Does home insurance cover a sewer backup?
In a 2009 press release, the Insurance Information Institute said some policies cover it and many do not, and that a sewer backup rider can be added. Coverage may have changed since then, so ask your agent and check your policy before you need it. Source
Related repairs
- Burst Pipe in House? What to Do First
- Clogged Drain? How to Unclog a Sink or Tub
- Frozen Pipes? How to Thaw Them Safely
- Garbage Disposal Not Working? Reset and Unjam It
- Leaky Faucet? How to Fix a Dripping Faucet
- Low Water Pressure in House? How to Find the Cause
- No Hot Water in House? What to Check First
- Toilet Keeps Running? How to Stop It Yourself
Last verified 2026-11-01
Sources
- University of Pittsburgh Safety Manual: Preventing Odors From Dry Sink Traps — Trap water seals out sewer gas, dry traps as a frequent source of the smell, and pouring a quart of water into unused drains weekly or monthly
- ATSDR/CDC: Hydrogen Sulfide ToxFAQs — Sewer gas smells like rotten eggs, is flammable, and people can lose the ability to smell it after 2 to 15 minutes at high levels
- Kansas State University: Dry Basements and Crawl Spaces — Sewage backups from plugged drains and overloaded sewers, and backflow valves
- NC State Extension: Inspecting a House — Raw sewage smell, soggy drainfield soil and slow drains as septic warning signs; pumping every 3 to 5 years
- Wisconsin Public Service Commission: Natural Gas Consumer Safety — Natural gas odorant smells like rotten eggs, sulfur or garlic, and leaving before calling
General information, not professional advice. Conditions, codes and prices vary. Turn off power, gas or water before any work, and hire a licensed professional when in doubt. Cost figures are our estimates, not quotes.