Leak Detection
Pinpoint where water is escaping inside walls, beneath floors or along the buried line before anything is opened up. Open page
Plain-English article
Tracking Down a Hidden Water Leak in Thornton, CO Homes
Half an hour and no tools is usually enough to narrow most hidden leaks. The key is to work in order, from the meter inward, so that each test rules out a part of the house.
By the Thornton Plumbing Co. team ·
Test the water meter
Close every tap, pause the ice maker, the washer, the dishwasher and the sprinklers. Then read the leak indicator on the water meter, often a small dial, triangle or star that spins with flow. If it moves, water is going somewhere.
For a more exact test, note the meter reading, wait an hour with no water used, and read it again. A change means a leak. The meter box is usually near the street or on a wall where the line enters the house.
If the meter does not move, the leak may be small or intermittent. Try the test again at a different time, and see the next steps.
Check the toilets
Toilets are the most common source of a silent leak. Remove the tank lid, put some food coloring into the tank, and wait fifteen minutes without flushing. Dye reaching the bowl proves the flapper is leaking.
Listen for hissing after a flush, which suggests a fill valve problem. Replace the worn part, and recheck the meter. If you need help, toilet repair covers the usual fixes.
Walk the house
Look under every sink, behind the toilets, around the water heater, near the washer hoses and under the dishwasher. Feel for dampness, look for rust on fittings and check cabinet floors for swelling.
Check ceilings for stains, especially below bathrooms. Check basement walls and floors, and the area near the sump pit and floor drain. Look at the water heater tank and its pressure relief valve discharge pipe for drips.
In winter, check exterior walls for frost or ice, which can point to a leak in an unheated space.
Look outside
Walk the yard. A spot where the grass is greener, the ground is soft or water pools without rain may be over a leaking service line or sprinkler pipe. Check the hose bibs for drips, and look at the sprinkler valve boxes for standing water.
If you have a sprinkler system, shut it off at the control and retest the meter. If the meter stops, the leak is in the irrigation system. See backflow testing for related outdoor equipment.
Usual leak spots and a quick check
Work through these in order. Each takes a few minutes.
| Place | Quick check | What it points to |
|---|---|---|
| Water meter | Watch the leak indicator with all water off | A leak somewhere past the meter |
| Toilet tank | Food coloring in the tank, wait fifteen minutes | A leaking flapper |
| Under sinks | Dry the pipes, then feel for new moisture | A supply line or a trap |
| Water heater | Look at the base and the relief pipe | A fitting or a failing tank |
| Yard | Look for soft or very green patches | A service line or sprinkler leak |
When it is behind a wall or under a floor
If the meter turns and you cannot find a leak, the pipe may be hidden. A plumber can isolate sections by closing valves and watching pressure, then listen for the leak and use a thermal camera to narrow the spot.
Learn more about the process on the leak detection page. If the pipe runs under a concrete floor, see slab leak repair.
What to do while you wait
Shut off the main valve if you cannot find the source and the leak is large. If it is small, you can leave the water on, but take a photo of the meter and track it daily.
Keep notes of what you tested and when. They help the plumber and an insurance claim. Fix easy things first, like a toilet flapper, and retest.
Check the places leaks hide most often
Start with the toilets, since a silent leak from the tank into the bowl is the most frequent hidden loss. Drop food coloring into each tank, wait fifteen minutes and look at the bowl. Next check under every sink for damp cabinet floors and corroded fittings. Look at the supply hoses to the washing machine and the dishwasher, which are common failure points when they age.
Go outdoors and inspect spigots, the sprinkler valve box and any low, soggy spots in the lawn. A valve that sticks open can run for weeks. Look at the water heater too, along its base and at every connection on top.
Use your senses and a few simple tools
Hold an ear close to the main and the water heater with the house quiet. A faint hiss can mean a pinhole or a running valve. A moisture meter, which is inexpensive, reads dampness in drywall and wood without cutting anything. Warm patches on a floor can point to a leak on a hot line under a slab.
Stains on ceilings, bubbling paint and a musty smell all point to moisture inside the wall. Photograph them and mark the edges with a pencil, with the date, so you can see whether they grow.
Know when to stop looking
If the meter keeps moving after you have ruled out every fixture, call. A plumber can isolate sections, listen along the pipe and use thermal imaging to narrow the spot before any wall is opened. That is faster and cheaper than guessing with a hammer. Our page on slab leak detection and repair covers leaks beneath concrete floors, a pattern seen in homes built on slabs.
Quick answers
Asked about finding a leak
Watch the meter with all water off. If it turns, there is a leak. A high bill, a damp spot or a hissing sound are other signs.
Toilets are the most common. Next are supply lines under sinks and the water heater.
Yes. A plumber can find it with listening gear and thermal imaging.
Yes for a large leak. For a small one, you can close the fixture's shutoff valve.
Connected services
Slab Leak Detection & Repair
Locate and mend a pipe that has failed beneath the concrete floor of a slab-on-grade house. Open page
Water Line Repair & Replacement
Mend or renew the buried pipe between the city's meter and your foundation when it breaks or corrodes. Open page
Related reading
Why the water bill is so high
A jump in the bill usually has a short list of causes: a leak, a seasonal change, an irrigation setting or a billing mistake. Here is how to sort them. Open page
Running toilet fix
A running toilet can waste thousands of gallons a year. The fix is usually a flapper, a fill valve or a chain, and takes minutes. Open page
Locating your main water shutoff
Know where it is before the flood. Here is how to find your main shutoff, test it and what to do if it will not turn. Open page
Meter still moving?
Ring the line and report the meter reading behavior you saw.