Close the nearest valve or zone to stop the water, then confirm the leak with a meter check and by locating the wet section. Most hidden wall leaks end with a small opening cut at the source, a repair, a test, and then drying and patching, which are usually separate trades.
How do you stop it first?
Find the valve that serves the area. In a restroom group that may be a stop at a fixture or a branch valve in a chase. If you can't tell which valve feeds the wall, the building's zone valve or main shuts it off. Planning a shutoff covers labeling valves and warning tenants.
Phoenix Water Services says knowing where your shutoff is, and testing it regularly, matters before you need it. It also warns customers not to shut water off at the city meter, because that takes a special tool and you may be held responsible for repairs to a damaged meter.
How do you confirm it is a wall leak?
EPA's guidance for commercial facilities recommends visual and auditory inspections: look and listen for unexpected water use, and read the meter with all uses off, then again an hour later. If the meter moves, water is escaping somewhere. A wet spot that grows after the fixtures are idle points to pressurized supply piping, not a drain.
EPA also notes that moisture meters can measure moisture in wallboard, wood and other materials and can be used to monitor drying. A plumber uses that kind of reading to choose where to cut, rather than opening the whole wall.
What happens next?
- 1The plumber opens a small access panel at the wettest point and traces the water to the pipe or fitting.
- 2The failed section is repaired or replaced, and the line is turned back on and watched.
- 3The wall stays open until it is clearly dry and the fix is verified.
- 4Drying and patching follow. Many commercial repairs need a permit check first.
Hidden moisture is the real cost. EPA's mold guidance warns that hidden mold can be a concern after known water damage and that investigating it takes caution and protective equipment. Wet drywall that stays closed is the common failure. Who handles cleanup after the plumber is worth deciding the same day.