What to do after a water backup occurs in your home

Reviewed by Jeanie Lentz

Updated March 15, 2024

It’s one thing to have a flooded basement full of water; it’s quite another to have one full of backed-up sewage.

Sewer backups aren’t necessarily the most destructive thing that can happen to your house, but they’re definitely one of the most disgusting. Here’s what you can do to prevent sewer backups, or respond effectively if you do experience one:


Thumbnail of the What To Do After a Gross Sewer Backup Occurs In Your Home video

What is a sewer backup?

A sewer backup occurs when wastewater moves the wrong direction through the sewer system—when dirty, disgusting water comes up through your drains, sinks, and toilets, rather than flowing down them.

All the dirty water from your plumbing fixtures has to go somewhere. Depending on where you live, your house might connect to a city sewer system or to a private septic system.

“Sewer systems connect entire communities and carry the wastewater to a treatment facility where it is treated and returned to the environment,” says wastewater expert Jeanie Lentz, of Lentz Wastewater Management Inc.

“Septic systems are, in some ways, a private mini sewer system, where effluent enters a septic tank, solids are separated from liquids, and wastewater is treated. Water leaves the tank and travels to the drain field area where it is slowly released into the soil and bacteria and viruses are removed.”

Both types of systems are susceptible to sewer backups.

What causes sewer backups?

There are several things that can cause a sewer backup, but we can separate them into two basic categories: either something is preventing the sewage from flowing, or there’s simply too much wastewater for the system to handle.

The first category can affect any home, whether it’s connected to a city sewer system or a private one. Your sewer system includes pipes that carry wastewater from the house to its destination—either the sewer main under the street or your septic tank.

If something blocks that pipe or otherwise prevents wastewater from flowing, eventually that wastewater will back up into the drains inside your home. Old homes are particularly susceptible to damaged sewer pipes, but there are many things that can cause a blockage.

“Sewer backups can be triggered by flushing items that should not be flushed—fats, oils, grease, wipes, etc.,” says Lentz. “They also can be caused by plumbing issues inside or under the house, improper seals in pipes, roots infiltrating pipes in your yard, traffic over sewer pipes or the deterioration of older pipes. If you have a septic system rather than sewer, the same issues can result in septic backups.”

Heavy rains can also cause sewer backups, particularly for homes connected to municipal sewer systems.

Most cities have wastewater systems that keep rainwater in one set of pipes and sewage in another set. Some cities have what’s known as a combined sewer system, which carries rain and sewage together.

When heavy rain falls, the sewer system can get so full of rainwater that it forces water (and sewage) up through the home systems to which it is connected. The result is a sewer backup in those homes.

Most of the time, wastewater systems need only the power of gravity to operate. But, some homes also have affluent pumps, which pump wastewater where it needs to go.

“If the pump malfunctions, this can also result in a backup,” says Lentz. “An alarm should sound if this is the source of your problem. If you hear the alarm, you’ll need to contact your local wastewater professional, and they may need to involve a plumber as well. If you don’t hear an alarm, check to see if the red light is on. This would indicate that you do have a problem with your pump, even though your audible alarm did not activate.”

Now that we’ve seen some of the causes of sewer backups, let’s turn to prevention.

How to prevent a sewer backup

Naturally, you want to prevent disgusting sewer backups from ever happening to your home. Fortunately for homeowners, preventing sewer backups isn’t complicated.

To start with, it can be as easy as installing a backwater valve, also known as a sewer backup valve or a backflow prevention device. This is installed between your house and the city sewer main. A backwater valve lets the wastewater flow in only one direction: away from your house. They’ll stop sewer backups caused by anything downstream of the valve.

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However, if you’ve got pipe blockages on your property, the backwater valve might not help you. You need to be proactive and keep your wastewater system clear.

The most common sources of blockage in a home sewer system are:

  • Deposits of fat or oil
  • Plant roots intruding into buried pipes
  • Unflushable products
  • Pipes that are sagging or have collapsed completely

Of course, you can’t actually see what might be blocking your wastewater pipes, as any blockages would be buried under your basement floor or your lawn.

But, you can always hire a plumber to scope out your sewage pipes with a special camera. You should have a professional do this every couple of years, or as soon as you notice any issues with your wastewater drainage.

What to do during a sewer backup

Dirty sink after a sewer back up that has not been cleaned

Sewer backups are gross—a mixture of water, human waste, mineral salts and garbage spilling into your home is the last thing you want to see.

The organic matter in raw sewage emits odorous gases and contains harmful pathogens. If your sewer backs up into the basement—or elsewhere—it needs to be cleaned up immediately.

Here are the steps you should take if you find your sewer backing up:

1. Diagnose and clear blockages

Once you realize that there is a water backup, check all of your sinks, toilets and wastewater pipes to locate any blockages. Try not to use your sinks or toilets until the blockage is cleared.

“Determine if the issue is isolated to one drain or toilet, or if it’s impacting all the drains and toilets in your home,” says Lentz. “If you are experiencing problems with only one drain, you likely have a plumbing issue. You may be able to resolve the problem yourself with a plunger or other device. If you can’t resolve it, contact a plumber.

“If you’re having problems with more than one drain or toilet, the issue is likely a sewer line leaving your home or the city’s mainline.”

If you can’t find a small blockage that you can easily clear, you’ve potentially got a larger issue on your hands. What do you try next?

“Determine if the issue happens only when you’re running water or if it occurs independently of running water,” says Lentz.

“If you experience a backup as you are running water or flushing toilets, that signals that the issue is due to the plumbing inside your house or the pipes leading to the sewer. Contact a qualified plumber or wastewater professional immediately.

“If the backup occurs when you’re not running water, the problem is likely triggered by the city’s lines. Contact your city immediately.”

2. Take some safety precautions

If you’ve got a widespread backup occurring, there are a few things you can do to make things safer while you await professional help.

First: electricity and water are a dangerous combination.

Don’t enter your basement when there is standing water present; wait until the power is shut off. If you need to enter the basement in order to shut off the power (as is commonly the case), take precautions first:

  • Wear rubber boots, safety glasses and a face mask.
  • Be sure you aren’t coming into contact with anything metallic that could conduct electricity.
  • Wear rubber gloves or use a wooden stick to shut off the electricity.

Open some windows in the flooded area to allow fresh air into the rooms and fumes to escape. You can also add a bit of bleach to any standing water to provide some disinfection.

Be sure to keep children and pets away from the affected area.

3. Document what happened

Document the damage by taking photos with your cellphone or camera.

“Be sure you also check with your insurance company,” says Lentz. “They often cover problems caused by sewer backups.”

If your home insurance policy does include coverage for water backups, you want to be able to illustrate the issue and the resulting damage. As soon as you’ve got a handle on the situation, get in touch with your insurance provider. They’ll help guide you through the process of remediating the damage.

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Cleaning up afterward

Two working men about to clean up a sewer backup

Once the blockage has been cleared and the pipes repaired, the waters should recede and allow for cleanup.

If your home suffered considerable damage, you probably want to hire professionals. The damage left behind by sewage is both disgusting and dangerous. If your home insurance policy does cover the water backup damage, they’ll help you pay for the remediation.

If you do decide to take on the cleaning and repairs yourself, don’t skimp on the personal protective equipment: wear an N95 facemask, safety goggles, thick rubber gloves, and rubber boots. Basically, you don’t want any sewage material to touch your bare skin or come anywhere near your mouth, nose, or eyes.

After you’re done cleaning each day, wash the clothes you were wearing, and shower with hot water and antibacterial soap.

The first step while you’re cleaning up is to remove everything movable from the affected area. Place everything somewhere that you’ll be able to easily clean afterward: a concrete floor, or a tarp in the backyard.

As you clean, start from the top and work your way down, hosing off furniture and walls to remove any clinging dirt. Wash all surfaces, including floors, with warm or hot water and an antibacterial disinfectant.

If there’s still standing water lying about you can remove it with a shop vacuum (if it’s a small amount) or rent a water pump (for larger pools).

What needs to be cleaned or tossed?

Pile of rugs and garbage from a sewer backup

You likely won’t be able to clean everything. Unfortunately, that’s just the reality of damage from sewer backups.

Anything that you can’t clean properly needs to be thrown away.

What needs to be tossed?

Anything with a porous or permeable surface will probably need to be discarded. The more porous a material, the harder it will be to clean and disinfect.

For example:

Carpet pads, carpets, cardboard boxes, books, mattresses, laminate flooring, unpainted drywall and cloth upholstery are all things that you won’t be able to clean sufficiently. Clothing and toys should be discarded unless they are cleaned and disinfected.

What can be salvaged and saved?

Semi-porous materials can generally be salvaged if you treat them immediately. These include cabinets, vinyl upholstery and wall coverings, hardwood floors, and painted drywall.

As for non-porous materials, they can almost always be saved, depending on how long they have been soaked by raw sewage. If the sewage is present for a while, there’s a greater chance that black mould could grow. Take care of these materials within a few hours of the damage, or they won’t be salvageable. The list of these materials includes tile, concrete, Formica and linoleum.

Does home insurance cover sewer or water backups?

Many home insurance providers do offer coverage for water backups, though you’ll often need to add the coverage specifically and pay extra.

Square One includes water and sewer backup coverage on every policy we sell.

It’s important to note, though:

If the water backup is caused by heavy rainfall or another weather occurrence, your insurer may treat it as a flooding event. That would mean your policy’s flood coverage applies—including any higher flood deductibles or even outright exclusion.

Check your policy wordings or speak to your provider if you’re unsure how your home insurance policy treats water backups.

Commonly asked questions

Can you get sick from a sewer backup?

If you have wastewater backing up into your home, it poses a serious health hazard.

“Bacteria and viruses are present in wastewater and can potentially make you sick,” says Lentz. “Water damage from the backup can lead to mold growth if not properly cleaned. Be sure to wear protective equipment—gloves, masks and eye protection—when cleaning up wastewater. For clean up, you may need a wet vacuum and steam cleaner, plus cleaning and disinfecting products.”

The damage from wastewater can be worse than just dirt; harmful bacteria live in the soiled materials and make you sick if you don’t properly disinfect them or dispose of them.

While the sewer backup is still in progress, you should also be wary of sewer gas: the nasty mixture of toxic fumes that sewage gives off. Sewer gas includes hydrogen sulfide, ammonia, methane, and other gases.

During a sewer backup, the gases are unlikely to be concentrated enough to cause harm, but even so, try to ventilate the affected area as best you can—especially in a basement where the gasses can’t easily dissipate.

How much does it cost to fix a sewage backup?

Sewage backups can be extremely costly; a severe event carries a price tag of at least $10,000.

That’s assuming the backup has damaged flooring, drywall, or furniture that will need replacement. A less severe backup that you can stop quickly may only cost a few hundred dollars.

Is a sewage backup an emergency?

A small water backup that’s affecting only a single drain isn’t an emergency—just make sure you shut off the water until you can unplug the line and restore drainage.

If you have water or sewage backing up through multiple drains and beginning to flood rooms, you can consider it an emergency (but not, like, a 911 emergency). You should contact an emergency plumber or your city’s engineering department immediately.

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About the expert: Jeanie Lentz

Jeanie Lentz is co-owner of Lentz Wastewater Management, Inc. and the third generation of the Lentz family to provide wastewater solutions for the Greater Piedmont area. She offers expert advice about best systems for specific situations, proper care, and maintenance, dealing with septic and sewer system blockage, troubleshooting, repair, replacement, and excavation. Jeanie received her master's degree from East Carolina University in Greenville, N.C., USA.


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