1. Your water bill jumps
A sudden or steady increase, with no change in how you use water, is often the first sign. Compare a few months of bills, ideally against the same months last year.
2. Warm spots on the floor
A leaking hot water line warms the slab above it. You might feel it barefoot, notice a pet that suddenly favors one spot, or find one area of tile warmer than the rest.
3. The sound of running water
With every faucet, toilet and appliance off, listen in a quiet house. A faint hiss or rush of water under the floor is a strong clue.
4. Damp or damaged flooring
Wet or musty carpet, cupping or buckling hardwood, and loose or cracked tile can all mean water is coming up from below.
5. Low water pressure
Water escaping under the slab never reaches your faucets. If pressure drops throughout the house, a leak is one possible cause.
6. A water heater that never stops
If a hot line is leaking, the water heater keeps running to replace the lost hot water. Listen for it firing up when nobody is using hot water.
7. Mold or mildew smells
Moisture trapped under flooring or along baseboards can cause a musty smell before you see any mold.
How to check your water meter
- Turn everything offEvery faucet, toilet, irrigation timer and water-using appliance.
- Find the leak indicatorOn most meters it’s a small triangle, star or dial that spins when water flows.
- Watch it for a few minutesIf it moves, water is leaking somewhere. If it stops when you close your main shutoff, the leak is inside the house. If it keeps moving, the leak is in the line between the meter and the house.
What to do next
If you suspect a hot water slab leak or see water inside, turn off the water and call a plumber with leak detection equipment. Avoid breaking up the floor yourself. Pinpointing the leak first keeps the repair small.
Tip: Take photos and note when you first noticed each sign. It helps with diagnosis and with an insurance claim.
Your repair options
- Spot repair: open the floor at the leak and fix that section of pipe.
- Reroute: run a new line through the walls or attic and shut off the old one.
- Repipe: replace the water lines if they’re failing in several places.
The right choice depends on the age and condition of your pipes and what flooring sits above the leak.