When some people see water collecting on the ceiling directly below a bathroom, they immediately go into the bathroom and look for the presence of water on the bathroom floor as a clue about the location of the leak. However, most of the plumbing in a bathroom is concealed behind walls or under the floor, making finding the leak more challenging.
You should not take bathroom leaks lightly, since the leaking water can lead to other problems. If enough water collects on the ceiling below, you will need to completely replace the soaked drywall since it will bow and warp. Moisture will warp the floor joists between the two rooms and can short out electrical devices such as light fixtures in the room below the bathroom. The presence of moisture can also lead to mould growth, which can further weaken the floor joists, ruin drywall and create a health hazard.
Determining the location of a leak in your bathroom's plumbing can present a challenge. Even though the water drips onto a specific part of the ceiling below the bathroom, the location of the leak could be in another part of the bathroom. When the water leaks out of a pipe in the space between the bathroom's floor and the ceiling below, called the subfloor, the water may run along the pipes for a distance before finally dripping off a pipe and falling to the ceiling below.
Leaking Shower Pan
The shower pan is the floor of the shower where the drain is located. The shower pan may be the source of the leak, since you will not notice any water leaking out of it while you are using the shower. A leak here will not leak water onto the floor in the bathroom, but the water will leak into the room below every time anyone uses the shower. To check the shower pan for a leak, stop up the shower's drain after you remove the drain cover, and then turn on the shower's faucet to fill the floor with an inch or less of water. If you cut a hole in the ceiling just below the shower you will see if the pan leaks or not.
Leaking Faucet Connections
The faucet connections inside the wall, whether they lead to a bathtub or shower faucet, can come loose, as can the connection for the shower head. When the connections come loose, the water will leak behind the wall, where you cannot see it, until you have water coming through the ceiling below. You can test for a faucet connection leak by running the faucet and collecting all of the water in a large bucket or other container. If you see more water collecting on the ceiling below, the faucet connections are the culprit; otherwise, the leak is somewhere along the drainpipes.