Do I have a water leak, and is it the roof or the plumbing?
Short answer. Check your water meter with every fixture off; if the meter or its leak indicator moves, you have a plumbing supply leak. If the meter is still but a stain grows only during rain, the roof, flashing, windows or siding are the likely source, and a stain that grows in dry summer weather near the attic air handler usually points to the HVAC condensate line.
The water meter test
- Turn off every faucet, appliance, ice maker and irrigation zone.
- Find the meter, usually in a box near the street, and look at its small leak indicator.
- If the indicator spins, or the reading changes over an hour or two, water is going somewhere.
- Close the main shutoff at the house. If the meter still moves, the leak is in the line between the meter and the house.
Rain or no rain?
- Only during or right after rain: roof, flashing, windows, doors, siding or gutters.
- Any time, rain or not: a supply line, drain, toilet seal, shower pan or appliance.
- Hot, humid days without rain: the HVAC condensate drain or pan.
- Cold mornings in the attic: condensation on nails and decking.
Location clues
- A ceiling under a bathroom: check plumbing first.
- A top floor ceiling near a chimney, skylight or exterior wall: check the roof first.
- A ceiling below an attic air handler: check the condensate line.
- A wet floor near the water heater: the tank or its relief valve.
Once you know the category, call the right trade: a plumber, an HVAC technician or a roofer. For roof leaks, see common roof leak causes; for condensation, see roof ventilation basics.