A bathroom that smells like sewer is most often a dry water seal in a drain you rarely use, and the fix is to pour water down it. But if the smell returns, only shows up after rain, or comes with gurgling drains, the trap is not the problem. It is air pressure in the drain system, and water will not fix that.

Where and when you smell it tells you the cause:

• Smell from one drain you rarely use (guest shower, floor drain, spare sink): the water seal has dried out. Refill it.
• Smell after heavy rain, or gurgling when you flush or empty the bath: a venting or pressure problem in the drain system.
• Smell at the base of the toilet: the seal between the toilet and the drain pipe has failed.
• Smell plus slow-draining water: a partial blockage, or a sagging pipe holding standing water.

Why does an unused drain smell like sewer?

Every drain has a bend in the pipe that holds a small plug of water. That plug is the only thing between your bathroom and the sewer. If a drain is not used for several weeks, the water evaporates and sewer air comes straight up.

Floor drains, walk-in shower channels, guest bathrooms and any flat you have been away from are the usual suspects.

The fix: pour a full jug of water into every drain in the bathroom, including the floor drain, and let the tap run for a minute. If the smell goes, that was it. Bleach and drain cleaner do not help here. They do not refill the seal, water does.

Why does my bathroom smell of sewer after heavy rain?

In the Netherlands the sewer in the street usually has no ventilation of its own. Street gullies have water seals so the street does not stink, so the air leaves the system through the rainwater pipes and roof vents of the buildings connected to it, according to a municipal sewer guide from Geldrop-Mierlo.

When it rains hard, the sewer fills with water and pushes that air back out. If the air cannot escape through the roof, it takes the weakest route, which is a water seal in your bathroom. That is why drains gurgle in a downpour, and why you can smell sewer on a day when nothing else has changed.

The same thing happens in reverse inside your home. A strong flush can pull water out of a nearby trap, and the smell appears right after you flush. A blocked roof vent makes both problems worse. An air valve (beluchter) on the affected drain lets air in at the right moment and stops the trap from being emptied. This is a plumber's job, because the valve has to match the problem.

When is it more than a dry trap?

If the smell stays after you have refilled every drain, look for these signs:

• Gurgling and slow drains: start with our guide on how to tell a blocked drain from a blocked sewer.
• Standing water in the pipe: in old buildings on soft ground, drain pipes sag and hold a pool of water. That pool blocks the air flow the system needs. Amsterdam's old canal houses are a classic case.
• Smell in several rooms at once: points to the main drain or the roof vent, not to one trap.

A strong rotten-egg smell that does not clear after refilling the traps is worth tracing quickly. Open a window while you do.

Frequently asked questions

Why does my bathroom only smell like sewer sometimes?

Usually because the cause depends on conditions. A dry trap smells after long gaps between uses. A pressure or venting problem smells after heavy rain or a strong flush.

How long does it take for a drain to dry out?

If a drain is not used for several weeks, the water seal can evaporate completely. Warm, dry rooms speed it up.

Does a sewer smell mean my pipe is broken?

Not usually. A dry trap or a venting problem is far more common. A damaged pipe tends to show up as a smell together with slow drains, damp patches or standing water.

Is sewer smell harmful?

Sewer air contains hydrogen sulfide, which causes the rotten-egg smell. A short whiff from a dry trap is not an emergency, but a smell that keeps coming back means there is a source to find.

Smell won't go away?

We are English-speaking plumbers in Amsterdam, Amstelveen, Den Haag and Utrecht. We trace the source, on site within 2 hours, 24/7. Drain and sewer jobs start at €129 incl. VAT. Call or WhatsApp 06-24356980.

Last updated: October 2026.