Quick Answer
A hidden supply leak may show up as unexplained metered water use, a higher bill, moisture, sound, or temperature changes before the source is visible. Start by confirming all known fixtures, toilets, appliances, irrigation, treatment equipment, and automatic users are off, then observe the meter and inspect for other clues. Drain leaks and intermittent leaks may not create continuous meter movement.
Common Symptoms
- •Water bill climbed with no change in use
- •Water meter moves when nothing's on
- •Warm spot on the floor
- •Musty smell or discolored wall
- •Sound of running water with nothing on
Possible Causes
- •Slab leak
- •Pinhole leak in copper
- •Failing supply line behind a wall
- •Underground service line leak
Safe Things You Can Check
Confirm fixtures, toilets, appliances, irrigation, water treatment, and automatic water users are off before interpreting meter movement.
If a known building-side shutoff can be operated safely, compare meter behavior before and after closing it; this can help determine whether unexplained flow is upstream or downstream of that valve.
Look for moisture, unusual sounds, temperature changes, or crawlspace/yard conditions, but remember that each clue can have non-plumbing causes.
WHEN TO CALL
If unexplained metered flow or other evidence suggests a hidden supply leak and the source is not visible, pressure/isolation testing and tools such as moisture, thermal, or acoustic equipment can help narrow the likely location while reducing unnecessary access.