Water
Water in the basement: causes and how to tell them apart
By ARO Restorations · Updated
Short answer
Water in a basement comes from one of four directions: up through the drains, in through the walls or floor, down from above, or from plumbing in the basement itself. When and where it appears tells you which, and the fix is different for each.
In this guide
Read the clues first
Before calling anyone, note three things. They narrow the cause quickly.
- When does it appear? During or after heavy rain, during a spring thaw, when a particular appliance runs, or all the time?
- Where does it start? At a floor drain, at the base of a wall, at a window, around the water heater or laundry, or in the middle of the floor?
- What does it look like? Clear, cloudy, dark or smelly?
The eight usual causes
1. Sewer backup
Water rises from the floor drain, a basement toilet or shower, often during intense rain. It may be dark and smell. Treat it as sewage. The fix is a backwater valve, and a camera inspection of the lateral if it happens in dry weather.
2. Sump pump failure
The pit is full or overflowing. Check the power, the float and the discharge line. See sump pump failure.
3. Seepage at the wall and floor joint
A line of damp or a trickle where the wall meets the floor, after prolonged rain or snowmelt. Groundwater is rising against the foundation. The fix is drainage: working weeping tile, a sump, and water directed away outside.
4. Cracks in the foundation wall
A vertical streak below a crack, usually worse in rain. Cracks can be sealed by injection or repaired from outside.
5. Window wells
Water enters at a basement window when the well fills. Clear the drain at the bottom of the well, fit a cover and check the grading around it.
6. Surface water from grading and downspouts
Water near one corner, often below a downspout. Soil that has settled toward the house, or a downspout that empties at the foundation, is the cause. This is the cheapest problem to fix.
7. Plumbing
Water near the water heater, laundry, a bathroom or under a pipe, unrelated to weather. A dripping fitting, a failed hose or a leaking tank.
8. Condensation
Damp on cold pipes, walls and floors in humid summer weather, with no puddles after rain. A dehumidifier and insulation on cold-water pipes deal with it.
A simple test for condensation versus seepage
Tape a square of plastic sheet or foil tightly to the wall or floor and leave it for a couple of days. Moisture on the room side means condensation from humid air. Moisture underneath means water coming through the concrete.
What to do with the water that is there
Whatever the cause, standing water should come out promptly and wet materials should be dried or removed within a day or two. Water from drains or from outside is treated as contaminated. See what to do when your basement floods.
Which causes insurance tends to cover
- Sudden plumbing failure: commonly covered
- Sewer backup and sump failure: usually an optional endorsement
- Surface water from outside: usually a separate optional coverage
- Seepage and condensation: frequently excluded
Who to call
- A plumber for drains, laterals, valves and fixtures
- A foundation or waterproofing contractor for cracks and drainage
- A restoration company to remove the water, dry the structure and rebuild
- Your municipality if you suspect the public sewer
Keep a simple log
If the water comes and goes, write down each time it appears: the date, the weather over the previous day, where the water was and roughly how much. Three or four entries usually show the pattern, and a contractor can work from it far faster than from memory.
More: flooded basement cleanup.
Questions people ask
Why is there water in my basement after it rains?
Rain raises the groundwater level and can overload sewers. The water is coming in through the wall and floor joint, cracks, window wells or up through the floor drain, or surface water is being directed at the foundation.
How do I know if basement water is from a leak or from outside?
A plumbing leak is unrelated to weather and usually near a pipe or appliance. Water from outside appears during or after rain or snowmelt, at walls, windows or drains.
Why is water coming up through my basement floor?
Either the groundwater level has risen above the slab, pushing water through cracks and joints, or the sewer is backing up through the floor drain.
Is water in the basement covered by insurance?
It depends on the source. Sudden plumbing failures are commonly covered. Sewer backup and overland water need optional endorsements. Seepage is frequently excluded.
Is a little water in the basement normal?
No. Even small, repeated amounts keep materials damp, which leads to mold and damage over time. Find the source and fix it.