How to check for a slab leak with the water meter test

Before you pay for detection, there is a free test you can do yourself with no tools: the water meter test. It can confirm whether a pressurized water line is leaking — including a line under your basement floor or slab — and it can narrow down whether the leak is inside the house, in the service line, or on the hot water side. It cannot pinpoint the leak, and it cannot catch drain leaks. This page gives you the full test the way it is actually done: the leak indicator check, the wait-and-compare, and the three isolation tests. If the test points to a leak, call (781) 483-8802 and we will connect you with a local plumber.

Step 1: Turn off all water, inside and outside

Go through the house and make sure every single water source is completely off:

• All faucets, showers, and hose bibs
• Toilets — do not flush during the test
• Dishwasher and washing machine — must be idle, not mid-cycle
• Ice makers, water softeners (verify they are not mid-cycle), and reverse osmosis systems
• Irrigation or sprinkler systems — shut them down at the controller

Anything using water during the test will move the meter and look like a leak. If the result surprises you, repeat the test once with everything confirmed off.

Step 2: Find your meter and check the leak indicator

Where the meter is in Woburn homes. In Woburn, the water meter is usually indoors, in the basement near where the main water line enters — often right by the main shut-off valve. If you do not find it there, check an in-ground utility box near the street, sidewalk, or property line; some homes have the meter there instead.

Read the leak indicator. Open the meter and look at the meter face. Find the low-flow leak indicator — usually a small red triangle, star, gear, or dial that spins when water flows. On a digital meter, look for a flashing flow icon. If the face is fogged or dirty, a damp rag usually clears it.

Watch it for 2 to 5 minutes.

• Completely still: you likely do not have an active continuous leak. A very slow leak can still hide below what the indicator shows, so move to Step 3 if you have symptoms.
• Turning or moving: water is actively moving through the system while everything is off. Something is leaking.

This indicator check is the fastest part of the test, and it catches leaks too small to hear.

Step 3: The wait-and-compare test (for slow leaks)

The indicator shows fast leaks. Slow leaks need the longer test:

1. Write down the exact numbers on the meter's main register (like a car odometer), or take a clear photograph of the meter face.
2. Leave the house alone without using any water for 1 to 2 hours. Longer is better if you can manage it — a slow leak moves the register less in an hour.
3. Take a second reading and compare.

- Numbers increased: water flowed while no one used any. You have an active leak. - Numbers unchanged: your supply lines are probably holding. If you still have symptoms, the problem may be a drain line, which this test cannot detect.

Step 4: Narrow down where the leak is

If the meter is moving, rule out the common culprits before assuming a slab leak. Work through these in order.

4a. Check the toilets first (dye test)

A leaking toilet flapper is the most common false alarm. Put a few drops of food coloring into the toilet tank without flushing. If color appears in the bowl after 15 minutes, the flapper is letting water slip away. Shut off the angle stops under the toilets and recheck the meter — if it stops, the toilets were the problem, not a slab leak.

4b. Close the house main shutoff valve (inside vs. outside)

Find the main water shutoff valve where the supply line enters the house (near an outer wall, garage, or foundation) and turn it off. Then watch the meter:

• Meter stops moving: the leak is inside the house, on the house side of the valve. Because Woburn homes are built over basement slabs, an indoor leak often means a pipe compromised under the floor or inside a wall.
• Meter keeps moving: the leak is outside, in the underground service line running between the meter and the house. That is a different repair from a slab leak.

4c. Isolate the hot vs. cold line

If the leak is confirmed inside the house, turn off the cold-water inlet valve on top of your water heater. If the meter stops, the leak is on the hot water line — which also fits a warm spot on the floor, since hot water leaks show up as warm patches. If the meter keeps moving, the leak is on a cold line.

What the test cannot tell you

• It cannot find the leak. It only says water is moving, and roughly which side it is on. Pinpointing the break needs pressure testing, acoustic listening, and thermal imaging — see our slab leak detection page.
• It cannot catch drain leaks. Drain lines are not pressurized, so a cracked drain under the slab will not move the meter. Sewage smells, slow drains on the lowest level, or damp spots near drains point to a drain problem instead — see sewer line slab leak repair.
• It can mislead if anything uses water. A running toilet, a softener mid-cycle, or someone flushing mid-test will move the meter and look like a leak. Repeat the test once if the result surprises you.

Other signs that back up the test

• A water bill that climbs with no change in use.
• Running water sounds with everything off.
• Warm or hot spots on the floor (hot water line leak).
• Damp carpet, cupped hardwood, or loose tiles.
• Musty smells or mildew near baseboards or in the basement.
• Low water pressure at several fixtures.

See our full guide to the signs of a slab leak for the complete list.

What to do if the test points to a leak

1. Shut off your main water valve if water is visible or the floor is wet. The valve is usually in the basement near the meter.
2. Turn off the water heater if the floor is warm — a hot water line may be the source.
3. Call (781) 483-8802. Tell us what the meter did and which isolation test pointed where. A plumber will confirm the leak with pressure and acoustic testing, pinpoint it, and give you repair options and a price before any concrete is cut. Detection usually runs $150 to $400.
4. Do not cut concrete to look for it. Cutting without detection usually means cutting twice.

Video note (optional, when filming)

This topic has strong video demand — short meter-reading clips rank well for it. A 60–90 second clip is enough: show the meter location, the leak indicator moving (or still), and the register reading. Film the indicator and the reading, not the whole 1–2 hour wait.