Why is there a sewage smell in my bathroom?
You walk into your bathroom and crinkle your nose as you detect the faint smell of sewage coming from ... somewhere.
At first, you think you're imagining things. You lean closer to the sink, the shower drain and the toilet as you try to identify the source of the offensive odor. You squeeze some cleaner into the toilet bowl and give it an extra scrub, even though you're certain you just cleaned it yesterday. The fragrance of the cleaner temporarily masks the smell, and you leave the room. Later, you catch another whiff as you walk past the bathroom door. This time, the smell is unmistakable, and no amount of scrubbing, running the fan or spraying air freshener is able to resolve it. So why is there a sewage smell in your bathroom?
The bad news is that any number of things can cause a sewage smell in your bathroom, and it can be difficult to pinpoint the source of the odor. Besides the obvious unpleasant smell, the methane in sewer gas can actually be flammable in large quantities, and breathing it in can be hazardous to your health.
The good news: Once you finally identify the reason for the sewage smell in your bathroom, it's often relatively simple and inexpensive to correct. Want your clean-smelling bathroom back? Read on!
Launch Video Take Home Handyman: Framing NailersPlumbing 101
To figure out what might be causing that awful smell, it helps to have a basic understanding of how the plumbing in your bathroom works. (Don't worry -- this will be quick!)
At some point, you've probably looked under the bathroom sink and noticed the U-shaped pipe that runs from your sink drain (B) to a larger wastewater pipe in the wall. One end of that big wastewater pipe runs down to your sewer or septic system (E); the other end leads all the way up through the roof (D), letting fresh air in while allowing any smelly sewer gases to vent out to the sky. And although you can't see it, the same basic drain setup is at work behind or beneath your tub and shower (C).
The U-shaped section of pipe below your sink is called a P-trap. When everything's working as it should, a small amount of water stays in the P-trap after you turn off the sink, empty the tub or flush the toilet. That little bit of water is enough to prevent gases from drifting out of the sewage system and into your house. Under normal conditions, those gases flow right past your bathroom and out through the vent pipe in your roof.
Sounds simple enough, right? But if you have a sewage smell in your bathroom, it usually means something in that very basic system has gone wrong. If you're lucky, it will be one of the easy fixes on the next page.
Easy Fixes
The first possible cause of a sewage smell in your bathroom is by far the easiest to fix. If your bathroom fixtures haven't been used recently (the sink in a guest bathroom or the tub in a bathroom with a separate shower, for example), it could be that the water in the P-trap has simply evaporated, removing the barrier between your bathroom and the gases in the sewer system. If that's the case, the solution is as simple as running some water to allow the P-trap to fill up again. If you smell the odor in a bathroom that's being remodeled, be sure to cap any open drain pipes until your new fixtures are installed.
If there's still a sewage odor after you've run plenty of water down all the drains, or if you notice a sewage smell in a bathroom that gets regular use, you might want to check for leaks in or around the P-trap. If even a small amount of water has leaked out of the bottom of the "U," sewage gases may be able to sneak in. Another possible cause that's kind of gross but fairly easy to resolve is a clog in the drain, since the clog itself can become smelly.
If the suggestions above don't lead you to the source of the sewage smell, you may be dealing with a more complicated issue like the ones on the next page.
Time to Call the Plumber!
So there's water in all the traps, you have no visible leaks and the pipes are free of clogs. What next?
It seems natural to assume that the toilet would be the obvious source of any sewage smells, but if there's water in the bowl, chances are the commode is not the problem. (The water here acts as a smell barrier -- just like the water in a sink's P-trap.) But if the bowl doesn't fill up as it should, the problem could be a broken seal, in which case it may be time to call the plumber.
Things get even trickier when the smell is coming from inside the bathroom but the problem itself is somewhere else. A roof vent blocked by a bird's nest, leaves, or snow and ice prevents fresh air from coming into the plumbing system and gives sewage gases nowhere to go but your bathroom drains.
A vent pipe that's been improperly installed or cut can also send offensive gases into your home. (Believe it or not, contractors have been known to vent these pipes into attics and crawl spaces instead of out through the roof.) And a cracked vent pipe can be even harder to track down, since the break is probably hidden somewhere within your walls. A plumber can help you locate a vent pipe leak with a device called a smoke machine, which fills the drain system with a harmless visible smoke. When the smoke finds its way out, you've found the source of the leak.
If you want to know even more about what's causing that sewage smell in your bathroom (and who wouldn't, really?), check out the links on the next page.