Basement flooding in NYC: getting out, pumping out, drying out

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If you live in a basement apartment, get out first

This is the part of basement flooding that costs lives. NYC Health reports that 14 people died from causes related to Hurricane Ida in September 2021, and most of them, 10 people or 71%, drowned in unregulated (illegal) basement apartments. During Superstorm Sandy in 2012, at least one third of the people who drowned at home were found in a basement or lived in a basement apartment.

Ida was a rain flood, not a storm surge. Rain fell faster than it could drain away, and the National Weather Service issued its first-ever flash flood emergency warning for New York City. Water can fill a below-ground room quickly, and the way out can be cut off fast.

• If water is coming in under the door or through the windows during heavy rain, leave for higher ground: an upstairs neighbor, the street level of the building, a friend’s home.
• Do not stay to save belongings or to move furniture.
• Do not go back down while water is still rising or the rain has not stopped.
• Take your phone and keys; everything else can wait.

The post on basement apartment flooding goes into this in more detail for tenants.

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Why New York basements flood

The Department of Environmental Protection names four kinds of flooding in the city, and three of them end in a basement:

• Sewer backups: heavy rain beyond the pipes’ capacity overflows from manholes, catch basins and the sewer connections in basements. During Ida, NYC Health says rain fell at up to 3.5 inches an hour in some areas, while the city’s sewers are built for 1.75 inches an hour.
• Groundwater flooding: saturated ground sends water in through cracks in the foundation or a leaking floor drain.
• Street flooding: blocked catch basins leave rain pooling in the street, and it runs down areaways, stairwells and garage ramps.
• Coastal flooding: high tide and storm surge, the cause of most of Sandy’s flooding, which can also push tidal water back into the sewer system.

NYC Health stresses that, unlike Sandy’s mostly coastal flooding, rainfall flooding can happen anywhere in the city. A basement in the middle of the Bronx can take on water in the same storm as one on the shore. It also notes a 200% increase in high tide flood days between 2000 and 2021, so shoreline basements see water more often too.

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What kind of water is it?

The source of the water decides how the cleanup goes, so it helps to notice where it came in.

Signs of where basement water came from

What you see	Likely source	What it means for cleanup
Water rising from a floor drain, toilet or shower, often dark or smelling of sewage	Sewer backup	Category 3: sewage. See the sewage cleanup guide.
Water seeping through the walls or the floor slab after days of rain	Groundwater	Often cleaner, but it has passed through soil; the provider’s inspection decides
Water pouring down the stairs or through a window well from the street	Street or storm water	Usually treated as contaminated; not automatically Category 3 under the IICRC’s 2026 position
Seawater or water from a creek or river	Coastal or river flooding	Category 3 under the S500 standard’s examples

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Power and gas before anything else

Basements hold the electrical panel, the boiler, the water heater and the gas meter in many New York houses, so a flooded basement is an electrical hazard before it is a cleanup job. The CDC’s guidance: if you can reach the main power switch from a dry place, turn it off. If you would have to step into standing water to reach it, call an electrician to turn it off instead. Never turn power on or off, or use an electric tool or appliance, while standing in water. And if you smell gas, turn off the main gas valve, open the windows and leave.

Have an electrician check the electrical system before the power goes back on. A boiler or water heater that sat in floodwater should be looked at by a qualified technician before it is relit.

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Pumping out a flooded basement

Once the rain has stopped and the power is safe, the water can come out. The CDC lists the tools: a wet-dry shop vacuum, an electric water transfer pump or a sump pump. For deep water, restoration providers generally use larger pumps and extraction equipment. The flood water pumping page covers pumping in detail.

Two warnings. If you use a fuel-powered generator to run a pump, the EPA says to use it only outside and at least 20 feet from the building, never in the basement, garage or a shed, because its carbon monoxide can kill in minutes. And if the ground outside is still saturated, water may keep coming in through the walls as fast as it is pumped out; a provider can judge when to start.

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Flooded basement cleanup, step by step

1. Photograph everything before it is moved: each wall with the water line, each item, the drain or wall where water came in.
2. Remove the water with a pump, extraction or a shop vacuum.
3. Take out soaked porous materials: carpet and pad, drywall and insulation below the water line, cardboard boxes, upholstered furniture. With sewage or floodwater these are usually discarded.
4. Clean hard surfaces: concrete, tile, metal. The EPA advises against mixing cleaning products or adding bleach to other chemicals.
5. Dry the space with air movers and dehumidifiers. The EPA’s guidance is to dry water-damaged areas within 24 to 48 hours to prevent mold.
6. Check before rebuilding: moisture readings should show the walls and slab are dry before new drywall or flooring goes in.

With sewage, the EPA says to call in a professional who has experience cleaning buildings damaged by contaminated water. The full cleanup order is on the flood cleanup in NYC page, and rebuilding afterward is covered in flood damage repair.

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Renters, owners and who handles what

If you rent, tell your landlord in writing and keep a copy. New York City requires owners of buildings with three or more apartments to keep tenants’ homes free of mold, and NYC Health says that includes safely repairing underlying problems like water leaks. Under Local Law 55 of 2018, those owners must fix the conditions that cause mold. If a landlord does not act, NYC HPD says a tenant can file a complaint online or call 311.

Your own belongings are a separate matter. FloodHelpNY notes that flood damage to a renter’s contents is not likely to be covered by renter’s insurance; flood insurance for contents is bought separately. If you own the building, FloodSmart says most homeowners insurance does not cover flood damage. Check your own policy or agent; the flood insurance basics page has the general rules.

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Keeping the next one out

After a basement has flooded once, it is worth asking why. DEP makes it mandatory for homeowners to disconnect downspouts from the sanitary sewer, because rainwater from gutters sent into the sewer can cause backups in basements. A backwater valve on the sewer line can stop sewage coming back in, and FloodHelpNY says a licensed plumber or engineer can tell you which type, if any, suits your home. FloodHelpNY also notes that filling in a basement needs an engineer and a permit from the Department of Buildings. The basement waterproofing guide and the post on preventing basement flooding cover these in full.

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Questions people ask