Sewer Backup in Basement: What to Do in the First Hour, Who Pays, and How to Stop It
Sewage coming up through a basement floor drain or toilet is a health hazard, not just a mess. Stop using water, keep people and pets away, find out whether it is your line or the city’s, call your insurer, and clean up safely. Here is the full plan.
Still stuck after this guide? You can ask a plumber online — see pricing, expert credentials and common questions first.
The Short Answer
If sewage is backing up into your basement, stop using all water in the house (no flushing, showers, laundry or dishwasher), keep children and pets away, and do not walk into standing water if outlets or appliances are submerged. Call your city's sewer department to ask whether the main is blocked, then a plumber if it is your line. Take photos and call your insurance company the same day.
Treat sewage as a health hazard: wear gloves, boots and eye protection, throw out soaked porous items, and disinfect hard surfaces. Standard homeowners policies usually exclude sewer backup unless you added a water backup endorsement.
A sewer smell without water is a different problem; see sewer smell in house.
What Should You Do in the First Hour?
| Step | What to do | Why |
|---|---|---|
| 1. Stop the water | Tell everyone not to flush, shower, run laundry or the dishwasher | Every gallon you send down the drain comes up in the basement if your line is blocked |
| 2. Keep people away | Children, pets and anyone with a weak immune system stay out of the area | Sewage carries bacteria and viruses |
| 3. Check electrical safety | If water is near outlets, cords, a furnace or a water heater, do not step in it. Shut off the power to the basement from the panel only if you can reach the panel standing on dry ground; otherwise call the utility or an electrician. | Water and live circuits are a shock risk |
| 4. Ventilate | Open windows if you can do it safely | Sewer gas is unpleasant and can be harmful in an enclosed space |
| 5. Document | Photos and video of the water, the drain it is coming from, and damaged items, with the date | Your insurer will ask for it |
| 6. Call the city | Call the city or utility sewer department (many have a 24-hour line) and ask whether there is a blockage in the main | If the main is blocked, a plumber cannot fix it from your house |
| 7. Call a plumber | If the city main is clear, the blockage is in your private line. A plumber can clear it through the cleanout and camera-inspect it. | Clearing the line stops more sewage from coming in |
| 8. Call your insurer | Report the loss, ask about coverage and whether they want you to use a specific cleanup company | Delays can complicate a claim |
A sewage backup is one of the few plumbing problems that is worth an after-hours call. See is this a plumbing emergency for the others.
Is It Your Sewer Line or the City’s?
In most US cities, the homeowner owns and maintains the private sewer lateral, the pipe from the house to the public sewer, often including the connection to the main. The city maintains the main under the street. Your city's website or sewer department will tell you exactly where the line is drawn.
| What you see | What it usually means |
|---|---|
| Only one fixture backs up, like one toilet or one sink | A local clog in that branch drain. See how to unclog a drain. |
| The basement floor drain or lowest toilet backs up when you run water upstairs | A blockage in your main building drain or lateral, often roots, grease or wipes |
| Sewage comes up even when no one is using water, and neighbors have the same problem | The public sewer main is blocked or overloaded, common after heavy rain |
| Backups get worse during storms | The public system is surcharging, or groundwater is entering your line. A backwater valve is the main defense. |
Does Insurance Cover a Sewer Backup?
- Standard homeowners policies (the common HO-3 form) usually exclude water that backs up through sewers or drains. Coverage normally requires an optional water backup or sewer backup endorsement, which many insurers sell as an add-on with its own limit.
- Flood insurance through the National Flood Insurance Program covers sewer backup damage only when the backup is a direct result of flooding in the area. A backup that is not caused by a flood is not covered.
- The sewer pipe itself is a separate issue. Some insurers and utilities offer service line coverage for repairing the lateral; a water backup endorsement usually covers the damage inside, not the pipe.
- Renters: the landlord's policy covers the building. Your own renters policy may cover your belongings only if it includes a backup endorsement.
Read your declarations page for "water backup" or "sewer backup", note the limit, and call your agent. If the city's main caused the backup, ask the city how to file a claim with it; many have a short deadline. Our guide to filing a home insurance claim covers documentation and adjuster visits.
How Do You Clean Up Sewage Safely?
For anything beyond a small amount on a hard floor, a professional water damage restoration company is the safer choice. Sewage is treated as the most contaminated category of water damage. If you do clean up yourself, follow CDC cleanup guidance:
- Protect yourself: rubber boots, waterproof gloves, eye protection, and keep cuts covered. Wash hands thoroughly afterward.
- Remove the water with a wet-dry vacuum or pump once the line is cleared and the power in the area is safe.
- Throw out porous items that cannot be washed and disinfected: carpet and padding, mattresses, upholstered furniture, pillows, stuffed toys and soaked cardboard. Photograph them first for your claim.
- Clean hard surfaces with soap and water, then disinfect. CDC guidance for walls and hard floors after floods is 1 cup of household bleach in 5 gallons of water.
- Never mix bleach with ammonia or other cleaners; the fumes are toxic. Ventilate while you work.
- Dry everything fast. EPA advises drying water-damaged areas within 24 to 48 hours to prevent mold. Use fans and a dehumidifier, and remove wet drywall and insulation below the water line.
If mold appears later, see mold in the house: health risks and removal.
What Causes Sewer Backups?
| Cause | Clues |
|---|---|
| Tree roots in the lateral | Slow drains that come back after snaking, older clay or cast iron pipe, big trees near the line |
| Grease, wipes and paper towels | Backups after heavy use. "Flushable" wipes are a common culprit. |
| Broken, sagging or collapsed pipe | Repeated backups, soggy patches in the yard, a camera shows a belly or break |
| City main blocked or overloaded | Neighbors affected, backups during heavy rain |
| Storm water entering the sanitary sewer | Backups only during storms; downspouts or a sump pump connected to the sewer where that is not allowed |
How Do You Prevent Another Sewer Backup?
- Backwater valve: a one-way valve on the main building drain that closes when sewage tries to flow back into the house. It is the single best protection for a basement. It must be installed by a licensed plumber, usually with a permit, and needs occasional inspection. Many cities, including Madison, Wisconsin and Albany, New York, offer rebates, and some require approval before work starts.
- Camera inspection: after a backup, have the lateral camera-inspected so you know whether roots or a break will cause the next one.
- Watch what goes down the drain: no grease, wipes, paper towels or feminine products.
- Disconnect downspouts and sump pumps from the sanitary sewer where local rules require it, and keep your sump pump working.
- Floor drain plug or standpipe: a simple temporary measure in an emergency, but it can push water out of the next lowest opening, so it does not replace a backwater valve.
- Add the endorsement: if your policy has no water backup coverage, ask about adding it now.
Call a plumber now if sewage keeps rising, it comes up with no water being used, you smell gas, or you have had more than one backup. Want help reading a camera report or a repair quote? Ask a plumber online.
Notes for Canada and the UK
- Canada: many cities offer subsidies for backwater valves and related basement flooding protection, Toronto among them. Check your municipality's program before hiring, since most require a permit and inspection. Water backup coverage is usually an add-on to Canadian home policies too.
- UK: in England and Wales, the water company has been responsible for most shared sewers and lateral drains outside your property boundary since 2011. Call your water company first if more than one property is affected. Your own drain inside the boundary is usually your responsibility.
Pro Tips
Frequently Asked Questions
What should I do if sewage backs up into my basement?
Stop using water in the house, keep people and pets away, and stay out of the water if anything electrical is wet. Call the city sewer department to check the main, then a plumber if your line is blocked. Photograph the damage and call your insurer the same day.
Who is responsible for a sewer backup, me or the city?
In most US cities the homeowner is responsible for the private lateral from the house to the public sewer, and the city is responsible for the main under the street. If the main is blocked, the city clears it. If your lateral is blocked, you hire the plumber.
Does homeowners insurance cover sewer backup?
Usually not under a standard policy. Most insurers require a water backup or sewer backup endorsement. Flood insurance under the NFIP covers a sewer backup only when it is directly caused by flooding.
Is sewage backup dangerous?
Yes. Sewage contains bacteria and viruses, and the water can hide electrical hazards. Wear gloves, boots and eye protection, keep children and pets away, and discard porous items that cannot be disinfected.
Can I clean up a sewage backup myself?
A small amount on a hard floor, yes, with protective gear, soap and water, and disinfection. For carpet, drywall, large areas or anything beyond a few inches, a professional restoration company is safer and often required by your insurer.
How do I stop my basement drain from backing up?
Have the lateral cleared and camera-inspected, stop grease and wipes from going down drains, and have a licensed plumber install a backwater valve. Check whether your city offers a rebate first.
Why does my basement floor drain back up when it rains?
Heavy rain can overload the public sewer, especially where storm water and sewage share pipes, and it pushes back into the lowest drains. A backwater valve is the main fix.
