Why Does Your Bathroom Sink Smell Only When Water Runs?4 min read

Most people imagine the bathroom sink to be one of the cleanest things in their home because soap is the most common thing that goes down the drain. Unfortunately, this makes it distressing when an awful smell comes from their sink whenever they run water. What can cause this issue, and how do you fix it?

A dry P- trap is the most common cause of a bad-smelling sink. Pouring (or running) water down the drain should re-fill the trap. If bacteria has built up in the pipes, pouring a half-cup of white vinegar down can help. If the smell is sulfurous (eggy), that’s actually coming from the water.

Let’s go through what can cause bad smells to come from a running sink in more detail to help you keep the bad smells limited to the toilet and other places you expect them.

Why Does Your Bathroom Sink Smell Only When You Run Water?

Woman washing her face with water above bathroom sink

Before we can get into how to stop your sink from producing these smells, we need to identify what’s causing the problem. So let’s quickly go through the most common things that can cause a sink to produce a bad smell.

Your P-trap is Dry

The P-trap is an essential part of your sink’s water system. The P-trap is the plumbing fixture underneath your sink that features a sharp bend.

This device is designed to keep debris from flowing into your water system and clogging it up somewhere you can’t reach it, but it also has another major purpose.

The P-trap is also designed to stop sewer gasses from getting into your sink. It does this by keeping water at the bottom of the P-trap so that the gasses can’t flow through. However, if your P-trap has dried up, nothing stops the sewer gas from flowing into your sink, potentially causing these bad smells.

There is Buildup in Your Sink

This issue may surprise some people since hand soap is the main thing many imagine going down their bathroom sink. However, things like hair and dead skin can accumulate in your sink and begin to create an odor.

It is also possible that someone has accidentally dropped something down your sink drain and created a blockage in your sink’s plumbing. This can cause buildup to accumulate in your sink quickly, which can also cause a sudden bad smell.

Your Sink Has Venting Issues

Many homeowners may not know that their sink is connected to the sewer system. It does this through a network of pipes in your walls leading from your sink to the sewer system.

The problem is that sometimes these sewer pipes can get clogged easily. Once these pipes get clogged, the sewer gasses within them will have nowhere to go but out your sink, resulting in a foul smell whenever the water runs.

Sulfurous Water

Some areas have water from a natural source that has sulfur dissolved into it. The water has picked up this sulfur as it permeated through the ground, so wells and other groundwater collection sources are especially prone to this.

The bad news is, you can’t make it go away, but the good news is it isn’t going to hurt anything. This water is safe to drink and use to wash and clean with, even if it has a bit of an eggy funk to it.

If only one of your sinks smells when running, then it’s much more likely a dry P-Trap or other issue, because sulfurous water would be in every sink in your house, not just one, if it was in the water source.

How Do You Fix and Prevent a Dry P-Trap?

As we mentioned in the previous section, a dry P-trap is one of the most common things that can cause nasty smells to come from your sink whenever you run the water. This is because the P-trap is the part of your sink designed to keep sewer gasses from escaping from your sink faucet.

The P-trap works by trapping water in your sink’s pipeline that preventing sewer gasses (and sometimes even insects) from passing through the pipelines and into your faucet.

This is why having dry P-trap results in bad smells. If there isn’t water in your P-trap, there’s nothing to stop the sewer gasses from passing through the pipes and into your faucet.

Thankfully, there is a straightforward way to prevent your P-trap from drying up. All you have to do is run water through your sink periodically. The main thing that makes a P-trap dry up is leaving the sink unused for a long time.

If your sink goes unused for a while, no new water will replace the water already trapped in your P-trap. Unfortunately, this means the water in your P-trap will slowly dry up. Simply making sure to run each faucet in your home for a little bit at least once a month prevents your P-traps from drying up.

However, if you are reading this article, likely, your P-trap is already dried up. So how can you fix a sink with a dried-up P-trap so bad smells will stop coming out?

To fix a dried P-trap, all you have to do is pour water into it. But before we can do that, we need to ensure that the P-trap is full of insects.

If your P-trap is dry, it can become a home for smaller bugs and insect larvae. You must pour about a cup of white vinegar (on Amazon) into your sink to ensure these are not in your P-trap.

Once your sink is bug-free, you’re finally ready to fill up your P-trap with water. All you have to do is pour about half a gallon of water down your sink’s drain. This will restore the barrier in your P-trap and prevent smells from coming out of your sink.

How Do You Get Rid of the Smell in Your Bathroom Sink Drain?

Plumber fixing a sink at home

As we mentioned before, besides the P-trap, one of the other most common things that can lead to nasty smells coming from your sink whenever water is running is due to debris and bacteria building up in your pipes. To fix this, we need to clean your sink.

Check the stopper

The first thing you need to check is your sink’s stopper. This is a common area for bacteria and other gunk to gather, so detach your stopper, pull it out, and clean it of any of this gunk that could produce your bad smells by wiping it down with the cleaner of your choice.

Clean the pipelines

Next, we need to clean out the pipelines. We mentioned this in our section on how to fix a dried P-trap, but once again, a great way to do this is to pour about a cup of white vinegar down your sink’s drain.

If you don’t have any white vinegar, you can also use the cleaning product of your choice. However, it’s imperative to avoid using any cleaning product containing vinegar and a cleaning product containing bleach. When these two chemicals react, they can create a noxious gas that can potentially be dangerous.

Call a pro

Finally, it is also possible that your sink is producing a smell due to a venting issue. In this case, it is best to call a professional plumber, as fixing this issue will involve tinkering with the pipes within your walls.

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Hi, I'm Ed, and I run BuildFanatic! I enjoy providing the best possible information on a range of home improvement topics.

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