The situation
Illustrative example. Not a real job or customer.
In a 1970s slab-on-grade tract home, a homeowner feels a warm patch on the hallway floor. The water bill has risen and the meter moves with all fixtures off, but there is no wet spot anywhere in the yard.
- Closes the house main shutoff: the meter stops moving
- Concludes the leak is inside, past the house valve
- Turns the water back on only as needed and calls a licensed plumber
The leak is downstream of the main shutoff, under the slab, likely on a hot water line.
Diagnosis in this example
- Isolate hot and cold.Closing the water heater's cold inlet stops the meter, pointing to the hot side.
- Locate.Acoustic and thermal clues place the leak under the hallway.
- Check the rest.The plumber notes the under-slab copper is original and has had one earlier repair elsewhere.
Repair under the slab or reroute
Break the slab and repair
- Opens the hallway floor
- Fixes one spot
- Leaves aging under-slab pipe in service
Reroute through walls and attic
- Abandons the under-slab hot line
- Requires wall and ceiling openings
- Avoids future leaks in that section
How the hypothetical reroute runs
- Planning
- Route mapped from the water heater through the attic to each fixture served.
- Before work
- Contractor checks permit requirements with the city.
- Install
- New line run and connected; under-slab section capped.
- Testing
- Pressure test and any required inspection.
- Finish
- Wall and ceiling openings patched.
Takeaway
Closing the house main shutoff during the meter test told this homeowner, in minutes, that the yard line was not the problem. That kept the focus inside the house and avoided pricing an unnecessary service line replacement.
Common questions
Is this a real house?
No. It is an invented example.
Is a slab leak the same as a main line leak?
Not necessarily. Here the leak was on an interior line past the house shutoff.
Should I turn off the water?
If water is reaching floors or electrical areas, close the main shutoff and keep people away from wet electrical areas.
General information for Fullerton, not a quote or professional advice. In an emergency, call 911.