The short answer
If you hear water running in the walls of a Northern Virginia house and nothing is on, it’s one of two things: something in the house is quietly using water on its own, or a pipe is leaking. A sound that keeps going for minutes is a pipe under pressure, which means a toilet refilling, an appliance, or a leak. A rush that stops in a few seconds is a drain carrying water from upstairs, or from next door in a townhouse. The water meter settles it in two minutes.
Is it worth chasing? Yes. A supply pipe leaking in a wall runs 24 hours a day, and the drywall soaks up every drop before you ever see a stain. Sounds are the early warning, the same way the lights and codes in error codes and warning lights at home are.
Things that sound like a leak and aren’t
- A toilet ghost flushing. A flapper that seeps lets the tank drain into the bowl until the fill valve kicks on for a few seconds, every so often, with nobody near it. It’s the most common cause, and it’s still a leak (toilet keeps running).
- The water heater refilling. After a shower or a load of laundry, cold water runs into the tank for a few minutes.
- The ice maker. A short fill through the line behind the fridge, every so often.
- A humidifier on the furnace. In winter, many run water over a pad whenever the heat is on and drain the extra down a small tube, a steady trickle for as long as the heat runs.
- A water softener. Most clean themselves in the middle of the night, and you can hear water running for an hour or more.
- Condensate. A high efficiency furnace makes water when it burns gas, and it trickles down a drain line or into a small pump that kicks on now and then.
- The neighbors. In a townhouse or condo, the drain stack in the shared wall carries their showers and flushes too.
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What the sound tells you
Swipe to see all columns →
Swipe to see all columns →
| What you hear | Usually | Worry? |
|---|---|---|
| A steady hiss or whoosh that doesn’t stop | Water under pressure: a toilet filling, an appliance, or a leaking supply pipe | Yes, if the meter moves with everything off. |
| A rush that stops in seconds | A drain carrying water from upstairs or next door | No, unless you find water or a stain. |
| A drip in one spot | A slow leak at a fitting, or sweat dripping off a cold pipe | Yes. Find the spot. |
| A bang when a faucet or the washer shuts off | Water hammer | Fix it. Every bang shakes the joints (water hammer). |
| Ticking or creaking when hot water runs | Hot pipes growing a little as they warm and rubbing on the framing | No. |
| A hum or whine from the pipes | Water pressure too high, often a failing pressure reducing valve | Yes. High pressure wears out every fixture (pressure reducing valve). |
Find it in ten minutes
- Walk to every toilet and listen at the tank. Then put a few drops of food coloring in each toilet tank, wait 15 minutes without flushing, and look in the bowl. Color in the bowl means the flapper is leaking.
- Check the water heater, the furnace humidifier, the softener and the fridge. If one is running, let it finish.
- Go out to the water meter with everything off and watch the leak indicator (how to read the water meter leak indicator).
- If it moves, shut the main valve at the house (finding your shutoff valves). If the sound and the meter both stop, the leak is inside, past that valve. Leave the water off and call.
- Feel the wall and the floor where the sound is loudest. A warm spot with no hot water running can be a hot line leaking (slab leak signs).
Signs on the wall
Water in a wall shows up last, not first. Watch for paint that bubbles or peels, drywall that’s soft when you press it, a stain that spreads, baseboard trim that swells or pulls away from the wall, a damp musty smell in one room, and a floor that cups or feels spongy near the wall. Any of those plus the running sound means the wall needs to be opened, and the sooner it’s opened the smaller the repair.
What it costs to find and fix
Finding a leak in a wall runs $200 to $500. A plumber who finds the exact spot first opens one small square in the right place, not a row of holes (how leak detection works). Often it’s one joint or one pinhole, and the fix is a short piece of new pipe.
If the house has polybutylene, the gray plastic pipe used in a lot of houses built in the 1980s and early 1990s, or old galvanized steel, one leak usually means more are coming. Replacing the lines runs $1,000 to $12,000. From about $17 a month at 0% APR for 60 months, the whole price financed, on approved credit. More on that in repiping polybutylene pipe.
If the meter is moving and you can’t find why, SwiftPro’s plumbers can. Our Water Test and Plumbing Safety Check is $29: a licensed plumber walks your plumbing with photos, checks the water heater and tests your water’s hardness at the kitchen table. If you already know something’s leaking, a plumbing visit is $49 in regular hours, and the price of the fix is in writing before we start. Booking a plumbing repair? The whole-house plumbing inspection is included, so the next drip gets caught too.
Get a plumber on it
Book a plumber online, call (703) 997-9757, or book the $29 plumbing safety check. We answer day or night. Rated 5.0 stars across 1,138 reviews on Google, Angi, Yelp, the BBB and Facebook, Virginia Class A license 2705192276.
Questions people ask
Why do I hear water running in my walls when nothing is on?
Most often a toilet refilling because its flapper is seeping, or the water heater, ice maker, softener or furnace humidifier using water on its own. If the water meter’s leak indicator moves with all of those off, a pipe is leaking.
How can I tell a drain from a supply leak?
A drain sound rushes and stops within seconds, because a drain only carries water while someone upstairs or next door is using it. A supply pipe is under pressure all the time, so its sound keeps going. The water meter tells you for sure.
Is it normal to hear water in the walls after flushing?
Yes, for a minute or so while the tank refills and the drain carries the water away. If it keeps running long after, or starts on its own later, the toilet needs a new flapper or fill valve.
How much does it cost to find a leak in a wall?
In Northern Virginia, leak detection at SwiftPro runs $200 to $500. Finding the exact spot keeps the opening in the wall small.
