P-1Pipes · sewer backups
Why does sewage back up into NYC basements?
NYC sewer backups mostly hit basements of one- and two-family homes in heavy rain; the owner is responsible for the house sewer out to the city main.
Which building is yours?
- Prewar walk-upReport sewage in the basement or a ground-floor drain to the super or owner at once; the house sewer and any backwater valve are the owner’s.
- Brownstone or row houseYou own the house sewer to the main. A backwater valve is only required in flood hazard areas, and only a licensed plumber should install one.
- Co-op or condo high-riseThe co-op board and property manager answer for the building drain and sewer; shareholders report backups to them, then 311 if it is the street.
- Two-family houseThe group most at risk: about 59,000 of the 74,000 properties DEP counts as vulnerable in big storms are one- or two-family homes.
- New-build condoThe condo association handles the building sewer; tell the property manager first. A unit’s own fixtures may be the owner’s under the bylaws.
Which building are you in, and who handles a backup?
Start with who is responsible for the pipe. The sewer lateral from your building to the city main belongs to the property owner, the same as the water line (DEP Service Line Protection page). In a rental walk-up, that means the landlord. Tell the super or owner the moment sewage shows up. In a co-op tower, the board and property manager deal with it. In a two-family house or a brownstone, the owner is the one who calls a licensed plumber and 311. Small houses carry most of the risk. When rain falls at 1.75 inches an hour, DEP reckons some 74,000 properties are exposed, roughly 59,000 being one- or two-family homes (DEP report on sewer backups).
Why does it happen in NYC?
About 60% of the city has combined sewers, where rain and household sewage share one pipe (DEP combined sewer overflows). In a heavy storm that pipe fills, and water can push back up the lowest drain it reaches, often a basement floor drain or toilet. DEP says wet-weather backups are now the majority. Blockages matter too. Grease caused 40% of the backups DEP investigated in 2023. Nearly one in three backups comes from problems in a building’s own plumbing, not the city sewer. DEP has cut backups from sewer blockages by 75% since 2010.
Legend: the numbers on this plate
- 60%share of the city with combined sewersDEP CSO page
- 74,000properties vulnerable to backups in a 1.75 in/hr stormDEP backup report, Dec 2024
- 59,000of those that are one- or two-family homesDEP backup report, Dec 2024
- 40%of 2023 backups DEP investigated that grease causedDEP backup report, Dec 2024
What should you do during a backup?
Stop using the drains on the lowest floor, and in a multi-unit building ask neighbors to hold off too. Report it to 311 right away. DEP asks people to report backups "not caused by conditions in your home", and then looks into the cause. If DEP finds the cause is inside the building or in the private connection, it records the backup as unconfirmed. The repair is then the owner’s job (DEP Rainfall Ready guide). Tenants should tell the super or owner as well as calling 311. For how repairs are split between owner and tenant, see who fixes what.
Is a backwater valve required, and does it help?
Only in some places. Section 715.1 of the 2022 NYC Plumbing Code requires backwater valves in buildings in designated flood hazard areas at risk of overflow. Anywhere else, a valve is the owner’s choice. DEP says a licensed plumber must install one, usually in two to eight hours, at a typical cost of $4,000 to $15,000. The owner then has to maintain it once or twice a year. DEP also warns that a misused or poorly kept valve "will cause" backups rather than prevent them. While the valve is closed, don’t use basement toilets, sinks or washing machines. That water has nowhere to go but your floor. DEP also points to fixture plugs for basement drains and toilets as a simpler, cheaper option.
| Building | Who decides | Usual first step | Notes |
|---|---|---|---|
| Prewar walk-up | Owner | Tenant tells super and 311 | Tenants should not touch the cleanout or drains |
| Brownstone or row house | Owner | Owner calls 311 and a licensed plumber | Backwater valve required only in flood zones |
| Co-op or condo high-rise | Board and property manager | Report to management | Lowest floors and basements most exposed |
| Two-family house | Owner | Owner calls 311; warn the tenant | Most at-risk group in DEP’s count |
| New-build condo | Condo board | Report to management | Check what the offering plan says about drains |
How can an owner lower the risk?
Keep grease out of sinks and drains, since it is the cause DEP finds most often in blockages. Keep the catch basin at the curb clear of leaves and trash, and report a clogged one to 311. DEP’s report also says roof downspouts must be disconnected from the sewer. DEP’s optional service line plan covers sewer line repairs for $143.04 a year on the water bill. When a sewer line breaks, DEP says owners typically pay $10,000 to $15,000 to fix it. Owners on septic, in parts of southwestern Staten Island, Queens and Brooklyn, face a different set of problems. See the Staten Island sheet.
Look up your own building
- 311 · report a sewer backup or a clogged catch basin at your address
- DOB License Search · check a plumber’s license before a valve or sewer repair
- ZoLa · whether your lot sits in a mapped flood zone
Questions people ask
Does the city pay for a sewer backup in my basement?
The city repairs its own sewer main. If DEP traces the backup to the private connection or the building’s plumbing, the repair falls on the owner. Damage claims against the city are a separate legal matter we don’t cover.
Can a tenant fix a backup themselves?
No. In a rental, the drain and the house sewer are the owner’s responsibility. Tell the super or owner and call 311, and stay away from the sewage.
Do new homes need a backwater valve?
Only in designated flood hazard areas, under Plumbing Code §715.1. Elsewhere it is the owner’s choice, and DEP says a licensed plumber must install it.
What is the most common cause DEP finds?
In the backups DEP investigated in 2023, grease caused 40%. Wet-weather backups, when heavy rain overloads the sewers, are now the most common overall.
Is there a city rebate for a backwater valve?
Not at present. DEP applied for a FEMA grant to pilot valves for about 124 homes in Brooklyn, and no subsidy program is open.
How this plate was drawn
Risk counts, causes and valve guidance come from DEP’s December 2024 report on preventing basement backups and its Rainfall Ready guide, checked 11 Nov 2026. We quote Plumbing Code §715.1 through DEP’s report, not from the code text itself. The service line plan fees show no effective date. Flood insurance and claims against the city are left out.
Sources
- NYC DEP — Protecting Your Home: tools to prevent basement sewer backups (Dec 2024) · at-risk counts, causes, backwater valve rules and costs · checked 11 Nov 2026
- NYC DEP — Rainfall Ready NYC homeowner’s guide · closed-valve warning, plugs, 311 reporting · checked 11 Nov 2026
- NYC DEP — Combined Sewer Overflows · 60% combined sewers · checked 11 Nov 2026
- NYC DEP — Service Line Protection Program · owner responsibility for the sewer line, repair cost range · checked 11 Nov 2026
- NYC Mayor’s Office of Environmental Coordination — CEQR Technical Manual ch. 13 · septic areas · checked 11 Nov 2026
Plate P-1 · revised 11 Nov 2026