Basement Sump Pumps in the Washington, DC Area

Where is the water coming from?

Basements across the region get wet in different ways, and the fix depends on the source. Look during a storm or right after one, and again after a dry spell.

The third row is easy to miss. A slow leak from a water heater, supply line or drain fitting can keep one corner soaked indefinitely, and a pump would only hide it. Arrange help tracing a hidden leak before buying equipment.

Why DC basements flood from the drain

About one-third of the District is served by a combined sewer system that dates from before 1900, where household wastewater and stormwater share the same pipes on their way to the Blue Plains treatment plant. DC Water explains that heavy storms and snowmelt can overload that system and push it to back up, and that homes at lower elevations without backflow protection are most at risk. The rest of the city, and most of the Maryland and Virginia suburbs, have separate storm and sanitary sewers, but a blocked or root-filled lateral can still send sewage into a basement.

Older rowhouses add another factor. DC Water's homeowner guide lists the ways a house can be tied into the sewer: foundation drains, a sump pump that empties outside or to the sewer, downspouts piped into the lateral, and basement floor, stairwell and yard drains. Every one of those connections is a path for water to come back in when the sewer is full.

How a backwater valve works

A backwater valve is a one-way valve on the sewer line that closes when the public sewer backs up, so sewage cannot flow into the building. According to DC Water, it closes automatically, needs no power and works whether or not anyone is home. A few points from DC Water's guidance are worth knowing before you install one:

• While the valve is closed, avoid running water in the house. Anything you drain has nowhere to go and can flood the basement from the inside.
• Some models add a manual gate you can close if the automatic flap fails while you are home.
• Alarms are available but need battery backup to work during a power outage.
• The valve needs cleaning about every six months, following the maker's instructions.
• In a building where several units share one lateral, the valve affects everyone's plumbing.

An indoor valve is easier to service but may mean breaking up part of the basement floor. An outdoor one keeps the mess outside but must sit within your property line. DC Water has offered backwater valve rebates in neighborhoods with a flooding history, after an engineering review of each property; check with DC Water about current availability. For homes with only a floor drain in the basement, a floor-drain backwater valve or a screw-in standpipe are lower-cost options. Ask about these with any sewer line repair in Washington, DC.

When does a sump pump make sense?

A sump pump sits in a pit at the lowest point of the basement. Foundation drains or a perimeter drain carry groundwater to the pit, and the pump lifts it out of the house. It is the right tool when:

• Water seeps in along walls or through the slab after storms or snowmelt.
• The lot is low or the water table rises in wet seasons, as in parts of College Park near Paint Branch and Indian Creek.
• Outside fixes, such as cleaning gutters, extending downspouts and grading soil away from the walls, have been done and water still gets in.

Fairfax County's flood advice starts with those same outside steps: clear gutters and downspouts, keep storm drains free of debris, and make sure the yard slopes away from the foundation. The County also points out that standard homeowners policies generally do not cover flooding.

What should you look for in a sump pump setup?

The pump

Submersible pumps sit in the pit and are quieter; pedestal pumps sit above it and are easier to reach. Either works if it is sized for the volume that reaches your pit. A plumber can watch the pit during wet weather or look at how often an existing pump cycles to judge capacity.

Backup

Summer thunderstorms and winter storms can cut power exactly when the pump is needed. A battery backup pump, or a water-powered backup where the code and the water utility allow it, keeps water moving during an outage. A high-water alarm costs little and gives warning before water reaches the floor.

Check valve and discharge line

A check valve on the discharge pipe stops pumped water from falling back into the pit. Outside, the discharge needs to go far enough from the house that it does not soak back toward the foundation. Fairfax County's policy for new homes calls for the outlet to be at least 10 feet from the foundation and, where the site allows, at least 10 feet from a property line in the direction of flow, without sending concentrated water onto neighbors, sidewalks or across curbs. In winter, a discharge line that freezes can back water up into the pit, so lines should drain fully and should not have low spots that hold water.

Where it should not drain

Groundwater pumped into a sanitary or combined sewer adds to the very overload that floods basements during storms. Rules on these connections vary by jurisdiction, so check with your water and sewer utility or local permit office before changing where a pump discharges. In DC, the Department of Buildings handles plumbing permits; in Montgomery and Prince George's counties, WSSC Water issues plumbing permits.

Keeping the pump ready

1. Before the wet season, pour a bucket of water into the pit and confirm the pump starts, empties the pit and shuts off.
2. Clear debris, gravel and silt from the pit and the pump's inlet screen.
3. Check that the float moves freely and is not catching on the pit wall or cord.
4. Test the backup battery and alarm, and replace the battery on the maker's schedule.
5. Walk the discharge line outside to make sure it is attached, open at the end and not crushed.

A pump that hums but does not move water, runs constantly in dry weather or cycles every few seconds needs attention before the next storm. Local plumbers handle sump pump installation and repair across the District, and you can also find help in Silver Spring or Alexandria.

If the basement is already wet

Shut off power to the basement before stepping into standing water if outlets or appliances are near it. DC Water warns that floodwater can carry disease and sharp debris, so wear boots and gloves. The EPA advises drying water-damaged materials within 24 to 48 hours to limit mold. For a sewer backup in the District, call the DC Water emergency line at 202-612-3400. If a pipe burst, our burst pipe checklist covers the first steps, and you can reach an emergency plumber in DC through this site.