A pipe that burst
A half-inch supply line under normal residential pressure moves several gallons a minute. The difference between finding it in ten minutes and finding it in four hours is the difference between a wet wall and a rebuilt floor.
- 1 The ceiling stain. The wet spot is the end of the path, not the start of it.
- 2 A burst supply line. Under pressure, so it does not wait for anyone to notice.
- 3 A frozen line. The run inside an exterior wall is the one that gives in January.
- 4 The washer hose. Braided or rubber, behind a machine nobody moves for years at a time.
- 5 The water heater. The tank opens at a seam, and it opens without warning.
- 6 Groundwater and backup. A high table pushing at the footing, and a drain that runs backwards in a heavy week.
The main shut-off, before anything else
In most New Jersey basements the main shut-off is on the street side of the foundation wall, near where the service enters, usually within a few feet of the meter. It is worth knowing where it is before you need it, and worth turning it once a year so it does not seize.
If the valve will not close, the curb stop in the street can be shut by the water utility. That call is worth making immediately rather than after twenty minutes of trying.
Why the wall gets opened even after it stops
Water inside a wall cavity has nowhere to evaporate to. Insulation holds it, the bottom plate wicks it, and the cavity stays at high humidity for weeks. Closing the wall back up over wet framing is how a plumbing repair becomes a mold problem three months later.
Proving it actually stopped
Once the valve is shut and the visible break is dealt with, there is a way to check the house rather than trust it. Close every fixture, turn nothing on, and go read the water meter. Most have a small triangular or star-shaped low-flow indicator that spins on the least trickle; if it is moving with the house quiet, water is still going somewhere. Note the digits, leave it an hour, and read again for the slow version of the same test.
This matters more than it sounds, because pressure that has been forcing its way out of one weak point has been leaning on every other joint in the same aging run. A second, smaller failure opening behind a wall that was just dried out is a common and thoroughly demoralizing sequence, and the meter is the one instrument in the house that will tell you about it before the ceiling does.