How to prevent basement flooding

Checked against FEMA and other official sources · Last reviewed October 8, 2026

How water gets into a basement

FEMA lists "four ways water gets into your basement": - Through the drainage system, known as the sump - Backing up through the sewer lines under the house - Seeping through cracks in the walls and floor - Through windows and doors, called overland flooding

Detroit's water department puts it simply: basements sit underground "where water seeps," foundations and drain tiles that aren't maintained can lead to flooding, and the sewer line from the house can fail and back up. The University of Minnesota Extension adds that the water table under a house can rise during floods or with the seasons.

Knowing which route the water takes matters for insurance too. See the insurance section below. [2][3][5]

Gutters, downspouts and grading

Roofs shed a lot of water. University of Minnesota Extension notes that a 1-inch rain drops 1,250 gallons on the roof of a 2,000-square-foot house, and that missing gutters and downspouts send rainwater toward the foundation, and "a downspout without an extender or splash block is worse than no downspout at all."

• Clean gutters and downspouts so roof water flows away from the house, FEMA says, and keep nearby ditches and storm drains clear.
• Extend downspouts. Minnesota says extensions should discharge water at least 4 feet beyond the wall.
• Grade the soil away from the house. Minnesota recommends a slope of at least 1 inch per foot for at least 6 feet. A FEMA guide for berms uses about 1 inch per foot for at least 10 feet. Fill in sunken spots next to the foundation.
• Seal cracks. FEMA suggests closing foundation cracks with mortar and masonry caulk or hydraulic cement, and sealing basement walls with waterproofing compounds.
• Cover window wells with sturdy covers.

Before you regrade or redirect water, check with your local building department, since changes often need permits. FEMA also asks you to talk with neighbors when your changes could send water onto their property. [1][2][3]

Sump pumps and battery backup

A sump pump collects groundwater from drain pipes around the foundation and pumps it out of the house, SDSU Extension explains. FEMA says sump pumps "can be an excellent defense against basement seepage and flooding" and says: "Be sure to choose a device with battery-operated backup, in case of electrical power failure."

FEMA's basement guide explains why the backup matters. Your basement can flood "when your primary pump stops working, when the power goes out or when torrential rains overload the pump beyond its capacity." A battery backup pump starts when water in the sump reaches its float switch.

Test the pump before the wet season. SDSU Extension's steps: 1. Unplug the pump, remove the lid, and check that the intake isn't clogged. Make sure the pump is unplugged before you touch it. 2. Plug it back in and slowly fill the sump with water. Make sure the float moves freely and the pump turns on at the right level. Repeat at least once more. 3. Let it run and listen. If it struggles or sounds irregular, it may be near the end of its life or need repair.

Send the water to the right place. SDSU says to discharge it at least 20 feet from the house if possible, never into the municipal sewer, a neighbor's lot, window wells or a septic drain field. Minnesota adds that the sump should have an airtight, childproof cover. [1][2][3][6]

Backwater valves and drain plugs for sewer backup

Floodwater and wastewater can back up into a home through toilets, sinks and floor drains. FEMA recommends sewer backflow valves "for all pipes entering the building," regardless of the potential flood elevation. Philadelphia's water department says backwater valves "let wastewater out of your home, but close to prevent water from coming back through your pipes."

What FEMA says to know first: - Have a qualified, licensed plumber install it. - Check with your local officials to find out whether your community permits these valves. - Valves can be jammed open by debris, so they need to be accessible for cleaning and repair.

Floor drain plugs are generally inexpensive, FEMA says, and its 2020 guide recommends them for basement floor drains. Its older basement guide adds limits: a float plug can be blocked open by small debris, and you shouldn't use a plug if you expect more than 3 to 4 inches of flooding, because it may cause ruptured pipes or a cracked floor. [1][2][7]

Water alarms and flood sensors

FEMA recommends a flood alert system. It says "a variety of flood sensors and other early warning devices can alert you to the risk of imminent flooding" so you can act before major damage occurs. FEMA's basement guide also notes that some newer backup sump pumps have a monitoring system that sounds an alarm when there's a maintenance problem. [1][2]

Move valuables and utilities up

• Valuables: Move important documents and valuable or sentimental items well above the likely flood level, or into watertight containers.
• Electrical: FEMA suggests raising electric panels, outlets, switches and wiring at least 1 foot above the potential flood elevation. This work should be done by a licensed electrician.
• Appliances: Consider moving furnaces and other HVAC equipment to a higher floor or the attic, and raising washers, dryers and water heaters above the ground floor. See water heater leaking for water heater care.
• Flooring: Use tile, vinyl or other flood-resistant flooring, with movable rugs instead of fitted carpet.

FEMA's basement guide adds a safety step: mark which breakers feed the basement and shut off the power before entering a flooded basement.

When a flood is coming, FEMA says to turn on sump pumps, close backflow valves, shut off electricity at the breaker panel, and move valuables to upper floors. [1][2]

Does insurance cover a flooded basement?

Flood insurance: FEMA says "basement coverage through FEMA's National Flood Insurance Program (NFIP) is limited." The NFIP treats any area with its floor below ground level on all sides as a basement. - Building coverage includes specific items, if installed and connected to power where needed. FEMA's examples: furnaces and water heaters, central air conditioners, sump pumps, electrical boxes, outlets and switches, unfinished drywall and attached stairways. It also covers cleanup, such as pumping out trapped floodwater. - Contents coverage, if you bought it, covers a few items in a basement, and only if they're connected to a power source: washers and dryers, portable or window air conditioners, and freezers and their food. - Not covered: finished floors and walls, furniture, electronics and other stored belongings.

The NFIP Claims Handbook also draws two key lines. A sump pump backup during a flood may be covered, but not a backup without a flood in the area. And water that seeps in from a flood may be covered, but not slow seepage from naturally rising groundwater.

Homeowners insurance: North Carolina's insurance department says water backup and sump overflow are not covered under a homeowners policy unless you add an endorsement, and it may not be offered unless you ask.

See what flood insurance covers and homeowners insurance and water damage. [4][8][9]

City programs that help pay for fixes

Some cities help homeowners prevent backups. Two examples: - Philadelphia's Basement Backup Protection Program provides free backwater valve installation and downspout changes for homeowners whose basements back up in wet weather. Your water bill must be current. - Detroit's Basement Backup Protection Program offered free backwater valves, sump pumps and downspout disconnections in 11 neighborhoods. Applications for its first two phases are closed and will reopen if more funding comes in.

Ask your city's water or sewer department whether a similar program exists where you live. [5][7]

Questions people ask