The coastal water intrusion decision tree

Work through these steps in order. Each answer narrows the source and points to the right next move. Safety first: if water is near outlets, cords or the panel, stay out of the area and have the power shut off by someone qualified.

Step 1: Close the main and watch

Close the house shutoff and wait ten minutes. If the dripping or spreading stops, the source is almost certainly plumbing. Go to pipe bursts or appliance leaks.

Step 2: Was it raining or blowing?

If water appeared during or just after a storm and the main made no difference, the source is likely the building envelope: windows, sliders, doors, roof, deck membranes or stucco cracks.

• Water at a window sill or below a slider: window and door leaks.
• Water on a ceiling under a deck or roof: roof and deck leaks.
• Only when wind came from one direction: wind-driven rain.

Step 3: Did it come in at floor level from outside?

Water flowing under doors or through a garage from outside is surface water. Treat it as contaminated and read flood cleanup. If you are near the lagoon or river, see low-lying areas.

Step 4: Does it smell like sewage or come up through drains?

That is a sewer backup. Stop using water and read sewage backup cleanup.

Step 5: No obvious event, just damp or musty?

Look for slow leaks, condensation or long-term seepage. Run the EPA WaterSense two-hour meter test with all water off. If the meter moves, there is a hidden leak. If not, the moisture is likely coming from outside or from humidity. Musty smell? See mold remediation.

Write it down

When it started, the weather, what you shut off and what changed. Photos at each step. This record helps the contractor and your insurer.

Worked examples

Example A: stain below a living room window after a windy night

Step 1: closing the main changes nothing. Step 2: it appeared during a storm from the southwest, and the window faces that way. Result: envelope leak at the window. Next: dry the wall below, then have the window and flashing inspected. See window and door leaks.

Example B: damp hallway carpet on a dry week

Step 1: closing the main, then watching the meter, shows the meter stops. Re-open, and the meter creeps with all fixtures off. Result: a hidden supply leak, possibly in a wall or under the slab. Next: a plumber with leak detection equipment, then drying.

Example C: water across the garage floor during heavy rain

Step 3: it came in under the garage door from the driveway. Result: surface water. Next: treat as contaminated, remove wet porous items, clean and dry, and look at drainage. See flood cleanup.

Example D: ceiling drip only when the upstairs shower runs

Step 1 does not apply cleanly because the leak is tied to use. Result: shower pan, drain or valve. Next: a plumber isolates which one; then dry the ceiling.

Tools that help you decide

• Your water meter. The EPA WaterSense two-hour test: note the reading, use no water for two hours, read again.
• A flashlight and your nose. Musty odor near a wall suggests hidden moisture.
• Weather history. Note storm timing and wind direction.
• An inexpensive moisture meter. Compare suspected wet spots with the same material elsewhere.

Why we built a decision tree

Coastal homes see more envelope leaks than inland homes, and the fix for an envelope leak is different from a plumbing repair. Getting the source right early saves money, avoids drying a wall twice, and keeps your insurance story straight. Many homeowners policies treat sudden plumbing failures, storm-created openings, gradual seepage and flood differently, and FloodSmart notes most homeowners policies do not cover flood.

When to stop diagnosing and call

• Water is near electrical equipment.
• A ceiling is sagging.
• Water came from a sewer or from outside at ground level.
• More than one room is wet.
• You cannot find the source within a few hours.

In any of these cases, send a request with your notes. The moisture map will narrow down the source quickly.

Keep the record as you go

Note each step's result with the time. Insurers and contractors both use these notes to decide on cause, and a written timeline is far more useful than memory a week later.

Sources, accessed Oct 16 to 17, 2026: EPA WaterSense: Fix a Leak Week · Ready.gov: Power outages · Ready.gov: Floods · IICRC (publisher of the ANSI/IICRC S500 water damage standard) · FloodSmart (NFIP)