You walk into the bathroom and there's a pungent, rotten-egg smell. Or you smell something foul in the kitchen that isn't coming from the trash. A sewer smell in your home is more than just annoying. It can indicate a problem in your sewage system that needs attention. And in some cases, it's also unhealthy: sewer gas contains hydrogen sulfide and methane, among other things.
In this article, we explain where sewer smell comes from, what the six most common causes are, and what you can do about it.
Where does sewer smell come from?
Your sewage system is designed to drain wastewater without you noticing it. Every drain in your home (sink, shower, toilet, washing machine) has a trap: a bend in the pipe that always holds a small amount of water. This water seal prevents air from the sewer system from entering your home.
If you smell sewer gas, something has gone wrong somewhere in that system. The water seal is no longer working, there's a leak in the pipe, or there's a blockage pushing gases back towards your home.
The 6 most common causes
1. Dried-out water trap
This is the most common cause and, fortunately, also the easiest to fix. If you don't use a drain for a long time (for example, a guest toilet, a utility room sink, or a floor drain in the garage), the water in the water trap evaporates. Without this water seal, there's a direct open connection between the sewer and your home.
Solution: Run water for a few minutes in every drain you don't use regularly. Do this at least once every two weeks. The water trap will refill, and the smell will disappear immediately.
2. Clog in the drain pipe
A (partial) clog in your sewer can prevent gases from escaping properly through the vent pipe on the roof. Instead, they are pushed back through your drain pipes and enter your home through the weakest points.
Do you notice gurgling sounds or slow-draining water in addition to the smell? Then a clog is likely the cause.
Solution: For a simple clog, you can clean the siphon or try a plunger. If that doesn't help, or if multiple drains are slow, then have a specialist unclog the pipe.
3. Defective or missing water trap
Sometimes a water trap is broken, incorrectly installed, or completely missing. This can happen with DIY renovations, older homes, or after work by a plumber who didn't finish everything properly.
You'll notice a broken water trap because the sewer smell is constant, regardless of whether you run water or not.
Solution: Have the water traps checked and replaced where necessary. This is relatively simple work for a professional.
4. Ventilation problem
Every sewer system has a vent pipe, usually a pipe that goes out through the roof. This pipe ensures that the air pressure in the sewer system remains balanced. If this pipe gets clogged (by leaves, a bird's nest, or ice in winter), negative pressure builds up in the pipes. This negative pressure sucks the water out of your water traps, removing the odor barrier.
Solution: Check if the vent pipe on the roof is clear. If you can't reach it or are unsure, a technician can quickly check it.
5. Crack or break in the sewer pipe
A small crack in your sewer pipe is enough to allow sewer gas to leak into your home. You'll often smell it in specific areas: near a wall, in the crawl space, or in the basement. The odor can vary depending on the temperature and humidity.
A break in the pipe is harder to find because the pipe is usually under the floor or in the ground. With smoke detection, a specialist can pinpoint exactly where the leak is. Harmless smoke is blown into the pipe; where the smoke comes out, that's where the problem is.
Solution: Have the pipe inspected. Depending on the severity of the problem, the pipe can be repaired, or replacement may be the best option.
6. Sewer smell from outside
Sometimes the sewer smell doesn't come from your own plumbing but from outside. An overloaded municipal sewer, roadwork, or a clog in your neighborhood's main sewer can cause sewer odors to rise into the air through manhole covers or street drains. This air then enters your home through open windows or ventilation grilles.
Solution: Temporarily close windows and ventilation grilles on the side where the smell is entering. Contact your municipality if the problem persists.
Sewer smell after a renovation
A common situation: you've just renovated, and suddenly you smell sewer gas in your home. This is almost always due to one of these three causes:
- Forgotten water trap: When pipes were adjusted, a water trap was not (re)installed.
- Damaged pipe: during renovation, a pipe was accidentally hit or shifted.
- Ventilation blocked: the vent pipe has been bricked up, cut off, or connected to an extractor hood (which is not allowed).
After a renovation, always have the sewage system checked if you smell a foul odor. The sooner you address it, the less damage and inconvenience you'll experience.
Is sewer smell in your home dangerous?
In small amounts, sewer gas is mainly unpleasant. However, with prolonged exposure or in enclosed spaces (crawl spaces, basements), it can pose risks:
- Hydrogen sulfide (H2S): the gas that causes the rotten-egg smell. In high concentrations, it can cause headaches, nausea, and dizziness.
- Methane: is flammable. In a poorly ventilated space, methane accumulation can theoretically pose a fire hazard.
- Bacteria and molds: moisture from a leaking sewer pipe promotes mold growth, which can cause respiratory problems.
With persistent sewer smell, especially in bedrooms or living areas, it is wise to have the problem resolved quickly.
When should you call a specialist?
Running water down all drains doesn't help? Then the cause is deeper, and you need professional help. Especially in these situations:
- The smell is continuous, not just occasionally
- You smell it in multiple places in the house
- The smell started after a renovation
- You also experience clogs or gurgling drains
- Moisture or water is visible in the crawl space
At RBNL, we come by for an inspection and solve the problem on the spot where possible. We work with fixed prices, no cure, no pay, and are available 24/7.
Experiencing sewer smell? Contact us →
Frequently asked questions about sewer smell in the house
Why do I smell sewer smell when it rains?
During heavy rain, the sewer system can become overloaded. Gases are then pushed back towards homes. Rainwater can also siphon out water traps if the ventilation isn't working properly. Does this happen often? Have the sewage system checked.
Can sewer smell come through the wall?
Yes. A crack in a sewer pipe running through or along a wall can cause sewer gas to seep through the masonry. Smoke detection can pinpoint the exact location.
Does an air freshener or scented candle help against sewer smell?
No. An air freshener masks the smell but doesn't solve the problem. The cause lies in your sewage system and must be addressed there. Don't live with a smelly house, but find the source.
What does it cost to get rid of sewage smell?
That depends on the cause. You can fix a dry water trap yourself at no cost. Replacing a broken trap costs very little. A camera inspection costs €180, smoke detection €180, or both together for €220. Check our price list for current rates.
I only smell sewage in the morning, how is that possible?
Sewage smell can be stronger with temperature differences. In the morning, when the house gets warmer, air from the pipes rises faster. Also, nighttime inactivity (no one using water) can cause the water trap to drop. In the morning, let water run briefly in all drains.
