Direct answer: Water coming under a door is usually caused by a failed bottom seal, worn side weatherstripping, a threshold gap, or water being driven and pooled against the door from outside. Start by figuring out whether the water is getting past the door seal or bypassing the frame from the surrounding opening.
Most likely: The most common fix is a bad exterior door sweep or compressed exterior door weatherstripping, especially if the leak shows up during wind-driven rain and the door otherwise looks intact.
Look for the path, not just the puddle. If the floor gets wet only during rain, this is usually a sealing or drainage problem at the bottom of the exterior door assembly. If the water shows up without rain, you may be chasing condensation, a nearby plumbing leak, or water traveling through the wall and only appearing at the door. Reality check: a small gap at the bottom can leak a surprising amount when wind pushes water at it. Common wrong move: replacing the threshold before checking whether the door sweep is even touching it.
Don’t start with: Do not start by smearing caulk across the inside edge or replacing the whole door. Blind caulking often traps water and misses the real path.
The floor gets wet after storms, often more on one bottom corner, and the leak is worse when rain hits the door directly.
Start here: Start with the bottom sweep, side weatherstripping, and outside pooling at the threshold.
Water shows up at the sill even without strong wind, or the outside landing stays wet against the door for hours.
Start here: Start by checking whether the threshold area is holding water or the exterior surface slopes toward the door.
The area near the door is damp in dry weather, or you see moisture after HVAC use or nearby plumbing use.
Start here: Treat this as a source-tracing problem first, not a door-seal problem.
The same corner stains, swells, or drips first, while the rest of the threshold looks mostly dry.
Start here: Check for a warped door slab, uneven threshold contact, loose hinges, or damaged weatherstripping on that side.
This is the most common leak path when water comes straight under the slab. The rubber or vinyl edge hardens, tears, shrinks, or stops touching the threshold evenly.
Quick check: Close the door on a sheet of paper at the bottom. If it slides freely in the wet area, the sweep is not sealing there.
If side or top weatherstripping is flattened, wind can push water past the edge and it can run down to the floor, making it look like a bottom leak.
Quick check: Look for shiny flattened spots, gaps at the latch side, or daylight around the perimeter with the door closed.
A good sweep still leaks if the door is sagging, the latch is not pulling the slab tight, or the threshold sits too low under one side.
Quick check: Check reveal gaps around the door and look for uneven contact marks on the threshold or sweep.
If the stoop, landing, or track area holds water against the door, even decent seals can be overwhelmed. Sometimes the water is entering around the frame and only showing up at the bottom.
Quick check: During or right after rain, look outside for standing water, clogged drainage paths, or water running toward the door instead of away from it.
You do not want to replace door parts for a problem that is really condensation, a wall leak, or water traveling from nearby.
Next move: If you confirm the moisture only appears during rain and starts at the door opening, keep going with seal and drainage checks. If water appears in dry weather or seems to come from the wall or floor edge instead of the door opening, stop chasing the door parts and trace the other source.
What to conclude: Rain-only leaks usually point to the door assembly or outside drainage. Dry-weather moisture usually does not.
Most under-door leaks happen because the exterior door sweep is no longer making full contact with the threshold.
Next move: If the sweep is damaged or not touching the threshold where the leak occurs, replacing the exterior door sweep or adjusting the threshold is the right next move. If the bottom seal looks even and tight, the water may be getting past the side weatherstripping or around the frame from outside.
What to conclude: A failed bottom seal gives water a straight path under the slab. Good contact at the bottom pushes you toward side sealing, alignment, or outside drainage.
Water often sneaks past the latch side or hinge side, then runs down and shows up as a puddle at the bottom.
Next move: If tightening hinges improves seal contact or you find crushed weatherstripping at the leak side, correct the alignment and replace the exterior door weatherstripping if needed. If the door is aligned and the perimeter seal still looks good, move outside and look for water loading the opening.
A door can leak even with decent seals if water is being held against it or driven around the frame from the exterior side.
Next move: If water only enters when it pools at the sill or hits one outside joint, fix that exterior water path before replacing more door parts. If no outside loading or bypass path shows up, go back to the door contact points and confirm the sweep and weatherstripping are truly sealing under pressure.
Once you know the path, the fix is usually straightforward. The key is to match the repair to the leak path and then test it before calling it done.
A good result: If the inside stays dry during the same kind of water exposure that used to cause the leak, the repair is holding.
If not: If water still shows up after a confirmed sweep and weatherstripping repair, the problem is likely outside the door slab itself and needs a closer frame or wall-opening inspection.
What to conclude: A successful retest confirms you fixed the path, not just the symptom. A failed retest usually means the water is bypassing the door assembly from the surrounding opening.
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That usually points to wind-driven rain getting past a weak seal or water pooling against the threshold. The most common culprits are a worn exterior door sweep, flattened exterior door weatherstripping, or outside drainage that holds water at the sill.
Usually no. Interior caulk may hide the symptom for a short time, but it often traps water and does not stop the real entry path. Find whether the water is crossing under the slab, getting past the side seals, or bypassing around the frame from outside.
Look for torn or hardened material, uneven contact, or a spot where paper slides through with the door closed. If the leak is at the same spot where the sweep does not touch the threshold, that is a strong match.
Then check alignment and outside water loading. A sagging door may not compress the seal evenly, and a good seal can still leak if water is pooling against the opening or getting behind the frame from an exterior joint.
Not usually. Start with the simpler, more common failure: the exterior door sweep and the exterior door weatherstripping. Replace the threshold only after you confirm the door is aligned and the bottom seal still cannot make proper contact.
Call for help if you find rot, soft flooring, a loose frame, water entering through the wall around the door, or an exterior landing that slopes toward the house. Those problems are bigger than a simple seal replacement and need source repair first.