How to Diagnose an Upstairs Plumbing Leak

Water from a plumbing leak does not always fall straight down.

When you see a plumbing leak on your ceiling, it may be easy to jump to a quick conclusion about the origin of the leak. Taking the time to diagnose the leak methodically will help you avoid thinking you have fixed the leak --- only for it to appear again. Water that leaks from a pipe, whether it is a water supply pipe or a drainpipe, may run along surfaces in the sub floor like pipes or joists for several inches or even feet before dripping onto the ceiling below.

Things You'll Need

• Drywall saw
• Bucket
• Flashlight
• Utility knife
• Caulk

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Instructions

1. Examine the area around each of the plumbing fixtures, looking for pooling water or signs of water damage. Look for signs of the floor bowing or being softer around the various plumbing fixtures.

2. Turn off any device in the house that is currently using water, including the dishwasher, washing machine or any running toilets. Go outside to your water meter and look at the small dial on the meter to see if it is moving at all. If the dial is moving, the leak is coming from one of the water supply pipes in the house.

3. Saw a small hole in the ceiling where the water is leaking and catch any standing water on the other side of the sheetrock using a bucket. Examine the subfloor with a flashlight, looking for signs of water damage that may help indicate the origin of the leak.

4. Plug the drain in your bathtub and shower, if you suspect it is the origin of the leak, and fill the tub or shower with at least 3 inches of water. Leave the water in the tub or shower for at least 10 minutes while you watch through the hole in the ceiling below for signs of leaking, indicating the seal between the drain body and the tub or shower is the source.

5. Drain the water from the tub or shower and watch for leaks from below, indicating the drainpipes are the source of the leak. Turn on the faucet so water flows out of the shower head and look for leaks, indicating the pipe behind the wall leading to the shower head is the source.

6. Splash different areas around your tub or shower with water, focusing on one area at a time. If you see leaking from below, dry the area and apply caulk to any joints or crevices after you remove any old caulk using a utility knife.

References

• Rocky Mountain Bathrooms: How To Find The Leak In Your Shower Or Bathtub
• "This Old House"; Mystery Shower Leaks; Richard Trethewey
• PlumbingInfo.org; Diagnosing an Upstairs Plumbing Leak