A water bill spike. There is a leak. The meter tells you if it is inside or underground.
The EPA puts the average household's leaks at more than 9,300 gallons a year. A hidden one in a wall or slab also feeds mold, so find it this week.
What is probably happening
- A running toilet. The EPA's food coloring test finds it in 10 minutes.
- An underground service line leak between the meter and the house. The meter spins with everything off.
- A slab leak under the floor: a warm spot, a sound of running water, or a damp patch of carpet.
- An irrigation valve stuck open, or a hose bib left on.
Do this in the next five minutes
- Turn every fixture and appliance off. Read the meter, wait 30 minutes with nobody using water, read it again. Any change is a leak.
- Close the main valve and read the meter again. If it stops moving, the leak is inside the house. If it keeps moving, it is between the meter and the valve, underground.
- Drop food coloring in every toilet tank. Color in the bowl after 10 minutes means a leaking flapper.
- Walk the yard and the slab for damp or warm patches. Listen at night for running water.
- EPA rule of thumb: a family of four using more than 12,000 gallons in a winter month probably has a serious leak.
Do not
- Do not ignore it. Gradual leaks are the classic insurance exclusion, so the longer it runs the more you pay yourself.
- Do not let anyone jackhammer a slab before an acoustic or pressure locate has narrowed the spot.
- Do not agree to a full repipe on the strength of a high bill.
Who to call
A licensed plumber, ideally one that offers leak detection
Leak detection uses listening equipment and pressure isolation. A plumber with that gear finds it. A restoration company only dries what it did.
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What it should cost
$150 to $400, averaging $280
Pinpointing a slab leak. Repair of the leaking pipe once found runs $150 to $4,700, averaging $500
Source: HomeAdvisor, slab leak repair cost, updated June 2026, and Angi, pipe leak repair cost, updated July 2026. View source
National published range, not a quote for your job. The full cost table for this trade is on the plumbing page.
Ask this contractor, on the phone, before anyone comes out
Tap each one as you ask it.
- What equipment do you use to locate, and will you mark the spot before any digging or cutting?
- Is the detection fee applied to the repair?
- Is it a spot repair or a reroute, and why?
- Will you give me a written report with the meter readings for the utility, which may adjust the bill?
End the call if
- A slab cut or a repipe quoted with no locate.
- No meter test offered.
- A whole house repipe recommended for one leak.