The Reason Your House Smells Like Sewer When It Rains

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A sewer system is used to collect wastewater from houses and businesses.

Sewer systems are normally made up of pipes that connect homes and businesses together.

Sewers, unsurprisingly, can be the source of these smells! To find out why it happens, and what you can do about it, read on!

Why Does My House Smell Exactly Like The Sewer System When It Rains?

A foul smell inside your house could be caused by several things. You might have a leaky pipe or drain.

Second, you might have an overflowing toilet (see also ‘How To Stop An Overflowing Toilet‘) or sink. You may have a clogged toilet or sink.

You might have a backed-up sewage system or a problem with your septic tank.

Sewer gas smells because rainwater washes away the dirt and debris that clogs up the pipes.

When this happens, the water gets into the pipes and mixes with the sewage. This mixture makes the sewer gas smell.

Sewer smells are caused by many things.

Cracked sewer pipes, dried-up drains, bad toilet wax rings, and clogged plumbing vents (see also ‘What Is A Plumbing Vent?’) are just some of them.

Rain also causes the water to rise, causing the air to become heavy, preventing sewer gas from flowing out but instead remaining low to the ground.

This results in a strong odor.

When it rains, there is an increase in the atmospheric pressure which makes air around your house become heavier than usual.

This increases the amount of water vapor in the atmosphere and reduces the amount of oxygen available to living things.

As a result, the air gets saturated with water vapor and smells bad.

Sewer gas is heavier than normal air. So when the temperature drops, the air gets saturated with sewer gas. This causes the odor.

Sewer gas smells are caused by the fact that the sewer lines are located underground.

When it rains, the water flows into the basement and then out of the house. In the basement, the sewer gas is trapped and stays close to the walls.

To prevent sewer gas from entering your house, make sure that all drains are free of obstructions and that the plumbing vent is clear.

Have any cracks in your sewer line or septic tanks repaired before problems occur. Don’t use a toilet that wiggles or wobbles.

Rainwater seeps into your basement because there is an opening in the foundation. You should call a professional plumber to fix this problem.

What Can You Do To Fix It?

If you know DIY, you could try to fix the problem yourself first before calling a plumber. If you are lucky, you might be able to solve the issue on your own. 

However, if the problem is caused by cracked pipes or septic tanks, you’ll need to call a plumber anyway.

These are some ways to remove the sewer gas smell in the home after it rains:

Check The Drain Traps

Drain traps are used to prevent sewage from backing up into your house.

They are located under sinks, toilets, showers, bathtubs, and washing machines. They are usually installed when installing new plumbing (see also ‘Indoor Plumbing – Get The Inside Scoop On Its History’) systems.

A P-trap is used to trap water at all times. Water flows into the P-trap and then flows down through the drain.

Sewer gas does not come up through the pipes because there is a barrier of water at the bottom of each pipe.

A P-trap is an important part of a plumbing system. It prevents sewer gas from entering your house.

If the trap is clogged, then sewer gas flows into your home.

Apart from fixtures, if you haven’t used your basement floor drain in a while, that could also be the cause of your problem.

You should open all the fixture faucet valves in your house for about 1 minute and then flush all toilets.

Pour about a gallon of water into the basement floor drain.

Rain changes the atmospheric pressure, making the air denser. This causes the sewer gas to rise up into the house.

Sewer gas occupies the lowest level of the vent. When the trap is full, the gasses are forced out through it.

Inspect Sewer Cleanout Plugs

The Reason Your House Smells Like Sewer When It Rains

Clean-outs are used to inspect pipes. Inside the house, a cleanout is usually placed in the basement. There is a hole in the floor drain on the wall. 

Sewer traps are designed to prevent gasses from escaping.

Sewer plugs must be tightened regularly to prevent sewage gasses from escaping into your house.

Bad Wax Ring

Toilets are made of porcelain or plastic. You should never use them if they start rocking around because it could cause sewage gas to leak out.

Wobbling toilets are dangerous because they break the wax ring seal. Sewer gas leaks through them when they start to rock.

You should get new wax rings if your toilet rocks. Wax rings are used to hold the water tank down inside the toilet bowl.

You should always check the wax ring before using the toilet. Wax rings cannot be used again.

A wax ring is cheap and easy to replace. Turn off the water to the toilet first before flushing.

Then use a sponge to remove the remaining water from the tank and the bowl then turn the water back on.

Replacing the wax ring is easy, but you’ll need to take off your toilet to do it.

Once you’ve removed the toilet, replace the wax ring. If that doesn’t work, call a plumber for assistance.

Bacteria And Decomposing Waste

Sewer smells are caused by the bacteria and decomposition of sewage in the sewer system, but also perhaps by trapped debris.

Dried Out Water Barrier

A dried-up water barrier in the sewer traps could cause a smell coming from your house.

You should check if there is any other reason why your house might smell bad.

Sewer leaks can be dangerous because they can cause sewer gasses to escape into your house.

These gasses can cause serious problems for you and your family.

Water And Pressure

Rainwater runoff goes down the drain. When it comes to sewage, it flows downward. Fumes rise as the water rises.

If You’re On A Septic Tank

Rainy weather causes atmospheric pressure changes, leading to the air becoming heavy, which prevents methane gas from flowing out of the septic tank.

This leads to an unpleasant smell similar to rotten eggs coming from the house.

Cold temperatures can cause water to drain out of pipes. This causes an odor in the house. When the temperature goes up, the odor goes away.

Sewer smells are often caused by blockages in the septic tank pipes.

New wastewater doesn’t enter the pipe because there isn’t enough room for it to flow into the pipe.

Old wastewater builds up in the pipes, and the gas produced by this buildup causes the smell.

Work done to the home or landscaping may have damaged the plumbing system, and the vents aren’t working properly.

Other Causes Of A Sewer Smell In Your Home

The Reason Your House Smells Like Sewer When It Rains

If your pipes are damaged, cracked, or broken, they could allow sewer gas to leak into your home.

Leaking pipes or improperly vented vents can cause sewer gas to leak into the house. 

Sewer gas can also leak into the house if vent pipes are installed near windows or air intakes.

Sewage from nearby septic systems can sometimes enter the house through cracks at the base of the foundation, especially if the house has suffered water damage.

Clogged drains are the most common cause of sewer backups.

Items such as grease, hair, soap scum, and other foreign objects can block pipes and cause them to back up into sinks and toilets (see also guide on how to fix a toilet backing up into a bath/shower).

When this happens, you may notice a strong odor coming from your bathroom. You should call a plumber if you suspect a problem.

Loose toilets can cause gas leaks in your home.

What Is Sewer Gas?

Sewer gas is a mixture of hydrogen sulfide (H2S), carbon dioxide (CO2) and ammonia (NH3).

If you’re experiencing a foul smelling odor in your house, you probably have sewer gas.

Hydrogen sulfide is a toxic chemical that causes health problems when inhaled.

It can cause eye irritation and other respiratory issues like a sore mouth and throat.

People who work around hydrogen sulfide may experience temporary effects like nausea and shortness of breath.

At high levels, people could suffer permanent damage to their lungs. Don’t wait until you’re trapped in a room full of sewer gas.

Call a plumber as soon as possible to fix your problem. 

Is Sewer Gas Dangerous?

Yes, breathing sewer gas is not safe and can cause serious health problems. Some gasses found in sewer gas greatly contribute to high-levels of toxicity.

Hydrogen sulfide is a poisonous gas. It causes organ damage and death. Ammonia is an odorous chemical used in cleaning products.

It irritates eyes and noses. High levels of ammonia can cause organ damage or even death.

Sewer gas is also dangerous because it contains both methane and carbon dioxide.

Ammonia is also flammable, but less than methane or carbon dioxide.

Therefore, sewer gas is more dangerous than either methane or carbon dioxide alone.

What Are The Problems With Exposure To Sewer Gas?

Sewer gas smells bad, but also causes many health problems. Sewer gas can be deadly if left untreated.

You should call an emergency plumber if you smell sewer gas in your house.

You should call an emergency plumber as soon as possible to address the problem.

How To Prevent Sewer Smell In Your House When It Rains

The Reason Your House Smells Like Sewer When It Rains

Preventing sewer gas leaks in your house is important because if left unchecked, the smell could be unbearable and the gas can be dangerous.

To prevent this, you should do these things:

Keep drains clean by regularly flushing them out. Make sure there is no blockage or debris in the drain line.

Install a vent pipe to allow air into the system. Have an inspection done every year to check for any problems.

Call a professional plumber when needed.

Make Sure Water Stays In The Sewer Traps

Plumbing traps should be kept full of water so they won’t dry up. To do this, add a few teaspoons of vegetable oil to each trap now and then.

Clean Out Your Drains

Clogged drains are incredibly common, but there are ways to prevent this problem.

You should regularly remove the drain stopper and clean the debris off, then set them aside, and use a plunger or pipe cleaner to clear out any remaining debris.

A pipe waste cleaner is an item used to clean pipes. To do this, you insert the pipe cleaner into the drain and then push it down as far as possible.

This pushes all the debris out of the drain. Then, you can either put the pipe cleaner back in or leave it in the drain. 

Either way, you should be able to get rid of all the debris in your drain.

When you’re done, you should flush the drain with hot water (boiling water) and replace the stoppers.

Make Sure The Toilet Isn’t Loose

Loose toilets can leak sewage into your home. You should check for leaks.

DIY Shower And Sink Drain Sewer Smell Removal

Baking soda is an effective solution for sewage smells. You can pour ¼ cup of baking powder into the affected drain. This will help to get rid of the odor.

This step requires you to add 1 cup of white vinegar into a bowl. Wait 2-3 hours for the mixture to cool off.

Then slowly pour a gallon of boiling hot water down the drain. After waiting 15 minutes, run cold water for 10 minutes.

Bleach works well to clean drains. You need to pour half a cup of bleach into the drain and wait two hours before rinsing it out with hot water.

After waiting two hours, rinse the bleach with another gallon or more of hot water.

Wait ten to fifteen minutes after this and then let the water stand until it cools down. This allows the remaining debris to fall away.

Mineral oil is used to slow down the evaporation of water. This helps prevent dry pipes and other problems. Cooking oil also does this job well.

However, always make sure to call a plumber.


Sewer gas can be extremely dangerous and can be the source of a sewer smell in your house.

There are some things you can do to help, but in many cases, you shouldn’t try to fix the problem yourself unless you’re an experienced DIYer or if you’ve previously dealt with sewer gas odors before.

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