Sewer backup: what to do now, what caused it, and who pays
Updated
The short answer
A sewer backup is wastewater flowing the wrong way out of your lowest drains — usually a basement floor drain or a lower-level shower — because the line downstream is blocked or the public sewer is overloaded. Stop using water, keep everyone away from it, and check whether neighbors are affected: that decides whether you call the utility or a plumber.
How urgent · Act today
Act today. Sewage carries bacteria and viruses, and it keeps coming for as long as anyone upstairs flushes, showers or runs the washer. Stop all water use now, keep children and pets out, and stay away from electrics in wet areas.
Health & safety
Treat backed-up water as sewage even when it looks clear. Wear rubber boots and gloves, keep children and pets away, and wash your hands before eating. Don't stand in water to reach an outlet, appliance or the electrical panel — if water is near electrics, call the utility or an electrician. Throw out porous things soaked in it: carpet and pad, cardboard, upholstered furniture, mattresses.
What causes a sewer backup
Several different problems produce the same symptom and need completely different fixes. Work down the list — each one names the check that rules it in or out.
- 1
A clog in your house's main drain
Grease, wipes and paper build up where every drain in the house joins. Because the blockage is downstream of every fixture, water from upstairs has nowhere to go but out of the lowest opening.
How to tell
Only your house is affected, it happens in dry weather, and it follows heavy water use — laundry, several showers, a dishwasher cycle. - 2
Roots, a belly or a break in your lateral
The pipe between the house and the public sewer is damaged or sagging, so it catches everything flowing through it. These backups tend to come back, often at shorter and shorter intervals.
How to tell
Backups recur after the line has been cleared, roots come out on the drain cable, or there are wet spots or lush grass over the line outside. - 3
A blockage in the public sewer
The utility's main in the street is blocked. Sewage from every house upstream then backs up into the lowest connected laterals.
How to tell
Neighbors have the same problem at the same time, in dry weather, often on the same side of the street. - 4
Stormwater overloading the public sewer
In older cities, sanitary sewers either carry stormwater by design or leak enough that heavy rain fills them past capacity. The main surcharges and pushes sewage back up the laterals into basements.
How to tell
It happens only during or just after heavy rain, several basements on the street are affected, and it clears as the rain stops. - 5
Downspouts or a sump pump discharging into the sewer
Roof drains, foundation drains or a sump pump connected to the sanitary line add huge volumes in a storm — sometimes your own, sometimes a neighbor's. Many cities prohibit these connections for exactly this reason.
How to tell
Backups coincide with storms even when neighbors are fine, and you can trace a downspout or sump discharge line into a drain rather than out onto the ground.
What to do in the first hour
The order matters. Stopping the flow and establishing whose problem it is come before cleanup, because every call and every insurance claim depends on the first thing you record.
- Stop all water use. Tell everyone in the house: no flushing, no showers, no laundry, no dishwasher. Everything that goes down a drain upstairs comes up the lowest drain.
- Keep people and pets away from the water and stay clear of electrics in wet areas.
- Check whether neighbors are affected — knock, or look at whether the street manhole is overflowing. That single fact decides the next call.
- If neighbors are affected or it's raining heavily, call your sewer utility's emergency number. Many utilities send a crew within hours to check the public main; New York City's Department of Environmental Protection, for example, commits to inspecting within six hours.
- If only your house is affected, call a plumber to clear the line from the outdoor cleanout. Ask for a camera run once it is flowing.
- Photograph and video everything before you clean: the water, the drain, the damage, the time. Keep every receipt.
- Call your insurer the same day, even if you are not sure you are covered — late notice is one of the easiest reasons to refuse a claim.
- Ventilate, then start cleanup safely or bring in a water damage restoration company for anything larger than a small area.
Is it the city's sewer or your line?
This is the question that decides who pays to clear it and who you call, and it can usually be answered in ten minutes without anyone looking inside a pipe.
| What you notice | Points to the public sewer | Points to your line |
|---|---|---|
| Neighbors | Other houses affected at the same time | Only your house |
| Timing | During or just after heavy rain | Any time, often after heavy water use |
| Pattern | Recurs with storms | Recurs after laundry days or every few months |
| Outdoor cleanout | Full to the top, and the street manhole is high | Full, but the street is flowing normally — the blockage is between the cleanout and the main |
| Who to call first | The sewer utility | A plumber |
If the outdoor cleanout near the property line is dry but your house drains are backed up, the blockage is between the house and that cleanout.
Who pays for what
Three different bills can come out of a backup, and they are paid by three different people or policies. Mixing them up is where most disappointment comes from.
Clearing the public main is the utility's job and costs you nothing. Clearing or repairing your own lateral — the pipe from your house to the main — is normally the owner's responsibility, and in most cities that includes the section under the sidewalk and street. Damage inside the house is an insurance question.
Claiming against a city for backup damage is possible but narrower than people expect. Cities generally have to have been negligent — failing to maintain a main they knew was a problem — and storm-driven backups are often treated as outside their control. Deadlines are short: New York City, for instance, requires a claim to its Comptroller within 90 days.
Will insurance pay for the damage?
Usually only if you bought the right endorsement before it happened. A standard homeowners policy excludes water that backs up through sewers and drains, which surprises most people the first time they file.
The add-on that covers it is usually called water backup and sump discharge or overflow coverage. It is typically sold in limits from $5,000 to $25,000 and commonly costs around $50 to $250 a year, sometimes with its own lower deductible. It pays for cleanup and damage inside the house. It does not pay to fix the pipe.
Flood insurance covers sewer backup only when it is directly caused by a flood in the area. A backup caused by roots or a clog with no flooding is not a flood claim.
Cleaning up safely
Small backups — a floor drain that overflowed across part of an unfinished basement floor — can be cleaned by a careful homeowner. Anything that soaked into drywall, carpet or a finished basement, or covers a large area, is worth handing to a water damage restoration company, partly because insurers expect professional drying documentation.
- Wear waterproof boots, rubber gloves and eye protection. Keep cuts covered.
- Remove standing water first, then everything porous that it soaked: carpet and pad, cardboard boxes, upholstery, insulation, mattresses. These cannot be reliably disinfected.
- Wash hard surfaces with detergent and water, then disinfect. Follow the dilution on the disinfectant's label and never mix bleach with ammonia or other cleaners.
- Dry the area within 24 to 48 hours with fans and a dehumidifier. That is the window the EPA gives for preventing mould growth.
- Cut out wet drywall at least a foot above the water line; it wicks moisture upward out of sight.
- If mould has already appeared over more than about 10 square feet, the EPA suggests professional cleanup.
Stopping it happening again
Prevention depends entirely on the cause, which is why a camera run after the line is cleared is worth the cost when the backup was yours.
- A backwater valve — a one-way flap installed in the lateral — lets sewage out and closes when the public sewer surcharges. It is the standard fix for storm-driven basement backups, and many cities subsidise installation.
- Keep grease, wipes (including 'flushable' ones), paper towels and hygiene products out of drains.
- Disconnect downspouts, foundation drains and sump pumps from the sanitary sewer where that is how they are plumbed.
- For a known belly or recurring roots, schedule maintenance cleaning before the line blocks rather than after.
- A threaded floor drain plug or standpipe can stop a basement floor drain overflowing during a storm, but only fit one after checking where else the water would then come up.
Frequently asked questions
- What causes sewage to back up into a basement floor drain?
- A blockage or overload somewhere downstream: a clog in the house's main drain, roots or a break in the lateral, a blocked public main, or stormwater overloading the public sewer. The floor drain is simply the lowest opening, so it's where the backed-up water escapes first.
- Is the city responsible for a sewer backup?
- The city is responsible for clearing its own public main. Whether it pays for damage in your house depends on local law and usually requires the city to have been negligent; storm-caused backups often are not. The lateral from your house to the main is normally the owner's responsibility.
- Does homeowners insurance cover sewer backup?
- Not a standard policy. You need a water backup and sump discharge or overflow endorsement, typically $5,000 to $25,000 of coverage for roughly $50 to $250 a year, bought before the backup happens. It pays for damage and cleanup, not for repairing the pipe.
- How do I stop a sewer backup in my house?
- Stop using water immediately so nothing more flows down. If the cause is a clog in your line, a plumber clears it from the cleanout. To prevent repeats, fix the underlying cause and consider a backwater valve if backups happen in storms.
- Can sewer backup make you sick?
- Yes. Sewage contains bacteria, viruses and parasites that can cause stomach and skin infections. Avoid direct contact, keep children and pets away, wear gloves and boots for cleanup, and wash your hands thoroughly.
- What is a backwater valve?
- A one-way valve installed in the sewer lateral that lets wastewater flow out to the public sewer but closes when sewage tries to flow back in. It's the standard protection against basement backups caused by an overloaded public sewer.
- Should I call a plumber or the city for a sewer backup?
- Call the sewer utility first if neighbors are affected or it's raining heavily — the public main is the likely cause and clearing it costs you nothing. Call a plumber if only your house is affected in dry weather.