What a hidden leak looks like
- A water bill that jumped without a change in household use.
- Hissing or running water heard in a wall or under the floor when everything is off.
- A warm spot on a tile or concrete floor (a hot-water line under a slab).
- Stains, soft drywall, bubbling paint or a musty smell.
- A patch of yard that stays green, soggy or sunken in dry weather.
- Water pressure that dropped for no clear reason.
The meter test, step by step
Stop all water use
Faucets, toilets, washer, dishwasher, ice maker, irrigation, softener regeneration.
Find the leak indicator
On most meters it's a small triangle or star dial that spins with even tiny flows. Smart meters may show flow on a display or an app.
Watch for 15 minutes
Any movement means water is flowing somewhere. Write down the main dial reading and check again after an hour or two without use for a slower leak.
Split the system
Close the main shutoff at the house. If the meter still moves, the leak is between the meter and the house, in the water service line. If it stops, the leak is inside.
Rule out toilets
Put food coloring in each toilet tank. Color in the bowl after 15 minutes is a flapper leak, the most common hidden leak of all. See toilet keeps running.
Where hidden leaks usually are
| Location | Clues | Who finds it |
|---|---|---|
| Toilet flapperMost common | Dye test positive; occasional refill sounds. | Replace the flapper. |
| Under a slabPossible | Warm floor, sound of water, cracks in flooring; common in slab homes in the South and West. | Electronic leak location, then a reroute or spot repair. See slab leak repair. |
| Inside a wall or ceilingPossible | Stains, soft drywall, musty smell near a bathroom or kitchen. | Moisture meter and thermal imaging, then open the wall at one spot. |
| Service line in the yardPossible | Meter moves with the house valve closed; soggy strip of lawn. | Repair or replace the line. |
| Irrigation systemPossible | Wet zone between waterings; meter moves with irrigation valve open. | Irrigation repair; check the backflow device. |
When to bring in leak detection
- The meter test shows a leak and the toilets pass.
- You see signs of water inside walls or ceilings.
- You suspect a slab leak. Locating it precisely avoids breaking up more floor than necessary.
More questions
Can a hidden leak cause mold?
Yes. A slow leak inside a wall or under flooring can keep materials wet for weeks, long enough for mold to grow before anything shows on the surface.
Does homeowners insurance cover hidden leaks?
Policies vary. Sudden damage is often covered; long-term seepage and the cost of finding the leak may not be. Check your policy.