Flooded basement: what to do and how to prevent it

What to do first in a flooded basement

This is the order I follow:

1. People first. Don’t go in if the electricity could be live in the water. If you can’t shut off the power from a dry spot, call an electrician, the fire department or your utility.
2. Gas. If you smell gas, get out. Don’t touch switches or use flames, and call the gas company from outside.
3. Find out what kind of water it is. A broken supply pipe isn’t the same as sewage or floodwater from outside.
4. Stop the source if you can do it safely: the main water valve, an appliance supply line.
5. Take photos before anything is torn out, for your insurance.
6. Get the water out and start drying as soon as possible.

What not to do

• Walk into water where there could be electricity
• Run a generator indoors
• Mix cleaning chemicals
• Use a household vacuum on standing water
• Point fans at visible mold
• Start tearing out contaminated materials without protective gear

The EPA recommends drying wet building materials within 24 to 48 hours, when possible, to help prevent mold growth. Treat it as a target, not a promise: some walls won’t be fully dry in two days. After a flood, the CDC also advises never turning the power on or off, or using electrical tools, while standing in water.

Clean water or contaminated water?

Restoration professionals sort water into three categories, set out in the IICRC’s water damage restoration standard. I don’t decide the category by whether the water looks clean. With Category 3 water, I’m much more aggressive about removing porous materials, and about containment and protective gear.

Categories from the ANSI/IICRC S500 standard for professional water damage restoration (fifth edition, 2021), as I explain them to homeowners.

Pumping it out

If the ground outside is still saturated, don’t pump all the water out of the basement at once. Daniel Mercer explains that the water inside may be helping to offset the pressure of the water outside. Remove it suddenly, and that difference can crack or lift the slab, push the walls inward and, in serious cases, contribute to a wall failure. If a wall is already bowed, cracked or displaced, if it’s an old unreinforced wall, or if there’s still floodwater outside, Daniel wants an evaluation before anyone pumps the basement out aggressively. He likes to remove water at a rate that lets the water outside drop too. If you pump water out and the level comes back up, the groundwater outside is still there.

There’s no single rule for every house. NDSU Extension advises removing about a third of the water each day. FEMA’s guidance on pumping out basements describes pumping down about 1 foot, waiting 24 hours and, if the level holds, removing 2 to 3 feet every 24 hours. Both are emergency guidance, not a building code or a structural calculation.

Drying out and what has to go

In my experience, three to five days of structural drying after the water is extracted is common on a typical residential job. That’s field experience, not a standard; it can be less, or much more. I don’t stop because the carpet looks dry. I want the materials that stay to be back to a reasonable level compared with similar materials that never got wet.

Equipment I use: extraction equipment, pumps for standing water, low-grain refrigerant (LGR) dehumidifiers, air movers, moisture meters and thermo-hygrometers.

What has to go depends on the water. With clean water and a fast response, some materials can be saved. With sewage or floodwater, much more porous material comes out:

• Drywall that’s soaked
• Wet insulation
• Carpet pad
• MDF
• Anything that can’t be cleaned and dried properly

For mold after a flood, see mold in basements.

Why basements flood

The causes I see most, roughly in this order:

1. Heavy rain with poor surface drainage, or groundwater
2. A sump pump that fails, or a power outage
3. A plumbing failure, a water heater or an appliance
4. A sewer or drain backup
5. Window wells and basement entrances
6. In coastal areas, flooding from outside

A flooded basement can have more than one cause at the same time. A storm, a power outage and a sump pump that stops working is a classic combination.

Preventing the next one

For a basement at risk from groundwater, in my order:

1. Gutters, downspouts and grading. Keep water from soaking into the ground next to the house.
2. Maintain the sump pump. Test it before storm season.
3. A battery backup or a second pump, especially if the basement depends on the sump to stay dry.
4. A high-water alarm.
5. Check the discharge, so the water doesn’t flow back toward the foundation.
6. Raise what you store. Nothing important directly on the basement floor.

Prevention depends on what caused the flood. If it was a sewer backup, I talk with a plumber about a backwater valve or another system suited to the house. I wouldn’t put plugs in drains at random without understanding the plumbing. FEMA’s mitigation guidance also recommends battery backup pumps and backflow valves, and warns that floor drain plugs shouldn’t be used where flooding can go above 3 to 4 inches, because the pressure can rupture pipes or crack the floor.

More on sump pumps and why water gets into a basement.

Does insurance cover a flooded basement?

In my experience, a sudden plumbing loss, like a burst pipe, is more likely to be covered by a homeowners policy. Water that seeped in over time often isn’t. If the water came from outside, you need flood insurance, and sewer backup or sump pump overflow is often covered only by a specific endorsement. I never tell customers their insurance will cover it. I tell them to document everything and call their insurance company.

Flood insurance through the National Flood Insurance Program covers only some things in a basement. According to FEMA, building coverage includes items such as furnaces, water heaters, central air conditioners, sump pumps, electrical outlets and cleanup, while finished walls and floors and personal belongings like couches and TVs in the basement aren’t covered.

DIY or call a pro?

You may be able to handle it yourself if

• It’s a small amount of clean water
• The source has been stopped
• The electricity is safe
• The water hasn’t gotten into the walls
• You can get the water out and dry everything quickly

Call a professional if there’s

• Sewage or floodwater from outside
• Any electrical risk
• A lot of standing water
• A finished basement, or wet walls and insulation
• Water that has been sitting for a long time
• Contamination in the HVAC system
• Visible mold
• Or if you simply can’t get it dry

As a reference, one Richmond restoration company lists $1,200 to $5,000 as the average cost of water damage restoration in the area, with drying times from 1 to 3 days for small jobs to 7 to 14 days or more for severe flooding (Voda, April 2025). Much of the bill is crew time, extraction, equipment days, monitoring, demolition and disposal; there’s little new material until rebuilding starts, so we don’t split materials and labor here.