Sewage Backup: What to Do First and How Cleanup Works

A sewage backup is wastewater from your drain or sewer line flowing back into the house, usually through the lowest drain: a basement floor drain, a shower or a toilet. Stop using water, keep everyone away from the area, and treat everything the sewage touched as contaminated. Sewage is the most contaminated kind of water a restoration company deals with, so cleanup is about safety and disinfection, not just getting the water out.

Key Takeaways

Stop running water in the house. Every sink, shower and flush adds more wastewater to a line that is already backing up.
Keep children and pets away from the affected area until cleanup is complete, as the CDC advises.
Under the IICRC S500 standard, sewage is Category 3 water: grossly contaminated and able to carry pathogenic, toxigenic or other harmful agents.
The EPA recommends a professional who has experience cleaning and fixing buildings damaged by contaminated water.
Standard homeowners policies typically do not cover sewer backups, according to the Insurance Information Institute. Coverage is bought separately or as an endorsement.

What Should You Do First During a Sewage Overflow?

The first minutes matter more for safety than for the house. In order:

Stop using water. The City of Pueblo’s wastewater department explains that if the blockage is in your service line, turning off all water in the building will stop wastewater from entering. If the blockage is in the public sewer main, turning off water in the house will not affect the flow, which is why the next calls matter.
Keep people and pets out. The CDC says to keep children and pets away from the affected area until cleanup has been completed. Pittsburgh’s utility adds that it is important to stay away from the contaminated area until professionals can assess the damage, and suggests checking with neighbors while you wait.
Deal with electricity safely. The CDC says never to turn power on or off yourself, or use an electric tool or appliance, while standing in water.
If you smell gas, leave. The CDC says to turn off the main gas valve, open all windows and leave the house immediately if you smell gas or suspect a leak.
Call your sewer utility or district if you are not sure where the blockage is. Pueblo’s guidance says to call the city first in that case. Then a plumber for a blockage on your side, a restoration company for the cleanup, and your insurer.

If the overflow came from a single toilet and stopped there, our guide to toilet overflow cleanup covers that situation step by step.

What Causes a Sewage Backup in a House?

Most backups come from one of a few causes, and knowing which one you have tells you who to call:

A blockage in your own sewer line. New York City’s Department of Environmental Protection says the most common cause of sewer backups there is blocked pipes, usually from grease, wipes and other items put down toilets and sinks. Pittsburgh’s utility adds tree roots and buildups of grease, hair and other solids.
An overwhelmed public sewer. Pittsburgh’s utility says backups are often caused by an overwhelmed sewer system during heavy rains. North Dakota State University Extension explains why the basement takes the hit: water seeks the lowest level, so when sewage or floodwater outside rises higher than the drains in the home, it comes in through them.
A flooded septic system. NDSU Extension notes that septic systems in rural homes can back up into the home if the system is covered by water.

How Can You Tell Where the Backup Is Coming From?

Wentzville, Missouri’s wastewater division says the problem is likely in your private sewer lateral if the backup only happens when you use water, or if drains empty slowly after you stop. Pueblo adds a second clue: water from a service line blockage is likely to be nearly clear or light gray with a mild odor, while wastewater from a sewer main blockage is likely to be dark or black with a strong odor similar to rotten eggs. It also says that if you are unsure of the source, call the city first, because plumbers lack the equipment to clear blockages in city sewer mains.

Who Is Responsible for the Sewer Line?

The pipe from your house to the public sewer main is usually yours. Platte Canyon Water and Sanitation District, based in Littleton, states that the sewer service line is owned and maintained by homeowners, including the connection to the district’s main. It tells residents with a backup to call the district first: if the blockage is in a district main, district staff restore service and work with the homeowner on cleanup; if it is in the service line, the homeowner must contact a plumber or contractor. Rules differ by city and district across the Denver metro area, so check with whoever bills you for sewer service.

What Should You Do If Sewage Backs Up in the Basement?

Pueblo’s wastewater department explains why basements take the hit: when flow in a sewer pipe is blocked, water builds up behind the blockage and exits at the lowest available point, and in buildings with basements the basement drains may be that point. It notes that backups normally affect only buildings with basements. The same first steps apply: stop using water, keep people out, and never touch electrical switches or appliances while standing in water. Then:

Call your sewer utility or district to find out whether the problem is in the public main or your own line.
Have a plumber clear or repair your line if the blockage is on your side.
Do not start pumping or mopping without protection. The CDC says to wear rubber boots, rubber gloves and goggles if sewage is involved.

If the water in your basement came from outside or from a clean supply line rather than a drain, our guide to basement water removal covers pumping and drying.

Is It Safe to Stay in a House With a Sewage Backup?

It depends on how far the sewage spread and whether the rest of the house can be kept separate from it. None of the agencies quoted here give a single yes or no answer, but they agree on the basics: keep children and pets away from the affected area until cleanup is complete (CDC) and stay away from the contaminated area until professionals can assess the damage (Pittsburgh Water).

The health side deserves its own article, but in short: the CDC says floodwater may contain sewage, and that exposure to contaminated floodwater can cause wound infections, skin rash, gastrointestinal illness and tetanus. Wash your hands after contact. For puncture wounds or wounds contaminated with feces or soil, the CDC says a health care professional should check whether you need a tetanus booster.

How Does Sewage Backup Cleanup Work?

The IICRC S500 standard, which restoration companies follow, classifies sewage as Category 3 water. It also lists toilet backflows that originate from beyond the toilet trap as Category 3, regardless of visible content or color. That is why sewage cleanup is a different job from drying out a burst pipe. For contaminated water, the EPA recommends calling a professional who has experience cleaning and fixing buildings damaged by contaminated water. Here is what the cleanup involves, based on CDC, EPA and utility guidance.

Protective Gear

The CDC says to wear rubber boots, rubber gloves and goggles if sewage is involved, and its disaster cleanup guidance also lists an N-95 respirator. When you are done, the CDC says to wash up with soap and water and to wash all clothes worn during cleanup in hot water and detergent, separately from uncontaminated clothes and linens.

Removing the Sewage and Contaminated Materials

Standing water and solids come out first; the EPA names a wet vacuum for removing water from floors, carpets and hard surfaces. Then the soaked materials. The CDC says to remove and discard drywall and insulation that has been contaminated with sewage or floodwater, and to throw away anything you cannot clean or dry quickly, such as mattresses, carpeting, carpet padding, rugs, upholstered furniture, stuffed animals, baby toys, pillows, foam-rubber items, books, wall coverings and paper products. Throw away any food that may have touched the water. Wentzville’s wastewater division also advises having a repair service inspect any electrical devices, furnaces or appliances the water reached.

Cleaning and Disinfecting Hard Surfaces

Pittsburgh’s utility says to wash washable surfaces with soap and water and then disinfect them with a bleach solution. The CDC’s bleach guidance gives the sequence: wash with soap and warm, clean water; rinse with clean water; apply the bleach solution; let the surface air dry. It specifies regular, unscented household bleach with a sodium hypochlorite concentration between 5 and 9 percent, at 1 cup of bleach to 5 gallons of water for household surfaces such as floors. Open windows and doors when working indoors. Never mix bleach with ammonia or any other cleaner. If you use a commercial disinfectant instead, follow its label.

Drying the Space

The EPA says to dry water-damaged areas and items within 24 to 48 hours to prevent mold growth. When electricity is safe to use, its homeowner guide says to use fans and dehumidifiers to remove moisture, but not to use fans if mold has already started to grow, because the fans may spread it. The CDC adds that fans should sit at a window or door and blow air outward. Afterward, the EPA recommends keeping indoor humidity below 60 percent, ideally between 30 and 50 percent.

If the area stayed wet longer than that, the EPA says to assume you have mold growth. Our guide to mold after a sewage backup covers what comes next, and our sewage cleanup service page explains how we handle the work. Once the space is clean and dry, removed drywall, flooring and trim are replaced as part of rebuild and reconstruction.

How Do You Choose a Sewage Cleanup Company?

Bob Vila’s guide to flooded basement cleanup calls a restoration company the best option after a raw sewage leak, because it has the safety equipment needed to work in a toxic environment. It suggests checking that the company is licensed to do business in your area and insured, looking it up on the IICRC website, reading online reviews, getting a detailed estimate and timeline from more than one company, and to keep shopping if a company asks for payment up front or seems too cheap.

How Much Does It Cost to Clean Up a Sewage Backup?

Bob Vila’s cost guide, published in February 2024, says most homeowners spend between $2,000 and $10,000 on sewage backup cleanup. It puts blackwater (Category 3) cleanup at an average of $7.50 per square foot for materials and labor, compared with $3.50 for clean water and $5.25 for gray water. These are national figures, not a quote. The size of the affected area, how long the sewage sat, and whether drywall, flooring or framing must be replaced all change the price, and clearing or repairing the sewer line itself is a separate plumbing cost.

Does Homeowners Insurance Cover a Sewage Backup?

Often it does not, unless you added coverage. The Insurance Information Institute says sewer backups are not covered under a typical homeowners insurance policy, nor by flood insurance, and that this coverage must be bought as a separate product or as an endorsement. Whether a particular loss is covered is up to your insurer and your policy wording. Call your insurer early and ask what documentation it needs. If the backup came from the public main, ask your sewer utility whether it has its own claims process. Our guide to filing a water damage insurance claim covers the process, and our insurance claims process page explains how we work with adjusters.

How Can You Prevent Another Sewage Backup?

Prevention is its own topic, but the basics are short. Platte Canyon district asks residents to flush only pee, poop and toilet paper, to put grease in the trash instead of the drain, and to have the sewer line inspected periodically. The Insurance Information Institute recommends a backwater valve, which allows sewage to go out but not come back in, and NDSU Extension says one can be installed in an existing home by a licensed contractor and should be inspected annually.

Frequently Asked Questions

What is sewage overflow cleanup?

It is the removal of sewage that has escaped a drain, toilet or sewer line, followed by removal of contaminated materials, disinfection of hard surfaces and drying. Because sewage is Category 3 water under the IICRC S500 standard, the EPA recommends a professional with experience in contaminated water.

What about a septic backup?

Treat it the same way as a sewer backup: keep people and pets away and treat the water as contaminated, since septic waste is sewage. NDSU Extension notes that septic systems in rural homes can back up into the home if the system is covered by water.

Can I use bleach to clean up sewage?

Bleach can be used on hard, nonporous surfaces after they have been washed and rinsed. Follow the CDC sequence and ratio above, use regular unscented bleach, and never mix it with ammonia or any other cleaner. Porous items such as carpet and sewage-soaked drywall are on the CDC’s discard list instead.

Getting Help With a Sewage Backup in Denver

Prime Restore Solutions LLC is an IICRC Certified Firm that handles sewage backup cleanup, disinfection, drying and repairs across the Denver metro area, 24 hours a day, 7 days a week. If sewage has come up through a drain or toilet in your home or business, call (720) 790-6056 or visit our Denver sewage cleanup page.

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