Water Dripping From the Ceiling: How to Find the Source
Water travels before it falls
This is the fact that makes ceiling leaks frustrating. Water leaves a pipe, runs along the top of the drywall, follows a joist, finds a low point or a fastener, and drops there. The stain can easily be several feet from the failure, and occasionally in a different room.
This is exactly why cutting drywall directly above a stain is often a wasted hole.
Narrow it by behaviour
If the drip is constant whether or not anyone is using water, it is a supply line, because supply is pressurised all the time. If it only appears when someone showers, runs the washing machine or flushes, it is a drain, a waste line, or a shower pan.
That one observation splits the possibilities in half before anyone opens anything, so pay attention to the timing before you call.
The usual suspects, by room above
Bathroom above: a failed shower pan or a leaking shower drain connection, a toilet wax seal, or a supply line to the vanity. Shower pan leaks are the most common and the most often misdiagnosed, because they only leak while the shower is running.
Kitchen above: the dishwasher connection, the sink drain, or the supply lines under the cabinet.
Nothing above but roof: this may not be plumbing at all. Water tracking down from a roof penetration, a flashing failure, or condensation from a duct in the attic all present exactly the same way.
Do this before anyone arrives
If the ceiling is bulging, put a bucket under it and pierce the low point with a screwdriver to let the water out in a controlled way. A bulging ceiling is holding a significant weight of water and it will come down eventually. Releasing it deliberately is far less damaging than letting it collapse.
Turn off the water to the fixtures above if you can, and stop using them entirely until the source is found.
Why locating is worth paying for
The alternative is opening drywall on a guess, missing, and opening more. Acoustic and pressure locating puts the opening within about a foot of the fault, which is one patch instead of three, and the drywall you do not cut is the money you save.
If any of this describes what is happening at your address right now, call (888) 809-6756. We answer 24 hours a day across South Carolina and will tell you what to expect before anyone comes out.