Sump Pumps & Basement Flooding

A sump pump sits in a pit in the basement floor and pumps groundwater out before it floods the house. It usually runs only in wet weather, which is exactly when the power may go out. A pump that fails without warning can cost thousands in damage, and a flooded basement is also an electrical and health hazard.

• Homeowners
• Renters
• Landlords

How a sump system works

• Drain tiles around the foundation collect groundwater and send it to the sump pit.
• When the water in the pit rises, a float switch turns the pump on. The pump pushes the water up a discharge pipe and out of the house.
• A check valve on the discharge pipe keeps water from flowing back into the pit when the pump shuts off.
• A sewage ejector is a different system that lifts wastewater from a basement bathroom to the sewer. It needs a sealed lid and a vent, and its maintenance is more serious.

Test it every few months

1. Make sure the pump is plugged into a GFCI outlet that works, and that the cord is in good condition.
2. Pour a few gallons of water into the pit, slowly, until the float rises.
3. The pump should switch on, empty the pit quickly and shut off without sputtering.
4. Check that water leaves the house through the discharge pipe, and doesn’t leak or flow back.
5. Test again before the wet season and before storms. Pumps often fail from sitting idle.

Maintenance

• Clean the pit and the pump’s intake screen, and remove sand, gravel and debris that can jam the float.
• Check that the float moves freely and isn’t stuck against the wall.
• Keep the pit covered to keep out debris, and to protect children and pets.
• Look at the discharge pipe outside and make sure it isn’t frozen, crushed or clogged.
• Replace the pump on schedule. Many last about 7 to 10 years, and sooner if they run a lot.
• Consider a high-water alarm that warns you before the pit overflows.

Discharge: send the water away from the house

• Run the discharge pipe so the water ends at least 10 feet from the foundation where possible, downhill and away from neighbors’ yards, or as your local rules require.
• Don’t connect it to the sanitary sewer unless local code allows it, because it is often prohibited.
• In winter, use a freeze-resistant discharge so it doesn’t ice over. A frozen pipe will cause the pump to run constantly and fail.
• Check that the water doesn’t pool and flow back to the house, or onto sidewalks where it can freeze. See Winter Storms.

Power outages and backups

• A power outage in a storm is when the pump is needed most. A battery backup pump runs for hours on a charged marine battery, and some include an alarm. Test it and replace the battery on schedule.
• A water-powered backup uses municipal water pressure and doesn’t need electricity, but it uses a lot of water and needs the right plumbing. A plumber can tell you if it’s allowed.
• A generator can power the pump. Never run a generator in a basement or garage, and connect it properly with a transfer switch. See Power Outages & Generators.

Electrical safety in a flooded basement

• Don’t touch electrical equipment or cords that are wet or in the water.
• Wait until a qualified person says it’s safe before turning power back on.
• Floodwater may carry sewage, chemicals and mold. Wear boots, gloves and a respirator for cleanup. See Disaster Cleanup and Home Mold.

If water gets in

1. Stay safe. Keep out of the water if power is on.
2. Move valuables, and call your insurance company. Take photos before you clean up. Standard homeowner policies often don’t cover flood or sewer backup unless you have a special rider or flood policy, so check your coverage.
3. Pump out the water gradually if the ground outside is saturated. Rapid pumping can damage the foundation.
4. Dry the area within 24 to 48 hours to limit mold. Throw out soaked carpet, padding and insulation.
5. Find the cause, and fix gutters, grading and drains. See Hurricanes & Floods.

Prevent flooding in the first place

• Keep gutters clear and downspouts discharging at least 5 to 10 feet from the foundation.
• Slope the soil away from the house.
• Keep window wells clear and covered.
• Know your flood risk, and consider flood insurance.

Sump pump checklist

• Pump tested with water in the last few months
• Plugged into a working GFCI outlet; cord undamaged
• Pit and intake screen clean; float moves freely
• Check valve works; discharge is clear and ends well away from the house
• Battery backup or alarm installed and tested
• Gutters, downspouts and grading directing water away

Last updated: October 4, 2026