Last reviewed and updated: 2026-09-24
If you can hear water running when every tap, appliance and toilet in the house is off, water is moving through your plumbing, and the only thing that moves water through a closed system is a leak. Because you can hear it, it is a pressurized supply line rather than a drain, most often a slab leak, a wall leak or a service line. Confirm it with the water meter, then close the main shut-off valve to stop the loss.
A sound you can hear means a pressurized line, so it is usually a slab leak, a leak inside a wall, or the buried service line. Start with the meter test to confirm it.
Confirm it in 20 minutes
- Silence the house. Turn off the icemaker, the water softener if you have one, and any humidifier. Wait for the HVAC to cycle off. Do not flush anything.
- Listen at different points. Put an ear to the floor in several rooms and to walls near plumbing. Where the sound is loudest is where to start looking.
- Go to the meter. If the low-flow indicator is turning with everything off, the leak is confirmed.
- Close the main house valve and re-check. Still moving means the leak is in the buried service line. Stopped means it is inside or under the house.
- Rule out the toilets. Food coloring in each tank, twenty minutes, no flushing. Color in the bowl means that flapper is your noise.
What it usually turns out to be
| Cause | Supporting clue | How common |
|---|---|---|
| Toilet flapper not sealing | Intermittent refill; dye test shows color in the bowl | Very common: check first |
| Slab leak | Sound loudest at floor level; sometimes a warm patch | Common in 1960s-1980s Marietta homes |
| Leak inside a wall | Sound localised to one wall; sometimes a damp or warm patch | Common |
| Service line leak | Meter still turns with the main closed; soggy lawn | Common |
| Irrigation valve not seating | Meter stops when irrigation supply is closed | Common, seasonal |
| Water heater relief valve discharging | Trickling at the drain line or pan | Occasional |
| Pressure-reducing valve failing | High static pressure reading | Occasional |
Do not wait to see if it stops. A pressurized leak runs 24 hours a day. The water bill accrues daily, and if it is under the slab or inside a wall, so does the damage. Closing the main shut-off between uses costs you nothing and stops both.
Frequently asked questions
Why do I hear running water when nothing is on?
Because water is moving through your plumbing, and in a closed system with every fixture off, the only thing that moves water is a leak. Since you can hear it, it is a pressurized supply line,most often a toilet flapper, a slab leak, a leak inside a wall, or the buried service line.
Could it just be a toilet?
Very possibly, and it is the cheapest thing to rule out. Put food coloring in each tank, wait twenty minutes without flushing, and check the bowls. Color appearing in the bowl means that flapper is leaking and is likely your noise.
Is this an emergency?
It is urgent rather than same-minute. Close the main shut-off valve to stop the loss, then book a normal-hours visit: you avoid an emergency premium and nothing gets worse in the meantime.
Where should I listen?
Put an ear to the floor in several rooms and to walls near plumbing, with the house as quiet as possible. Loudest at floor level points to a slab leak; loudest at one wall points to a leak in that cavity. It is a useful starting indication, though not a precise location.
Can a drain leak make this noise?
Not continuously. Drain lines are not pressurized and only carry water while a fixture is draining. A sound that continues with everything off is a pressurized supply line.