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How to Find the Source of a Water Leak

Water may be life, but it can also damage buildings and homes. A water leak, for example, can lead to the formation of an extensive and potentially deadly mold colony. Water damage can warp floors, discolor otherwise beautiful paint or tile, and even invite pests into the home. Obviously, you want to hire top professionals, but if not then you should carefully inspect the site on your own.

If you notice signs of water damage, don’t put off finding and fixing the source of the leak. It can be challenging to figure out where it’s coming from, but you have to locate it before it compromises the structural integrity and value of your house. Outlined below are several common sources of water leaks and how to find them yourself.

Water Flows Down

Water always flows from top to bottom. When you find evidence of a leak, look up. While evidence of water ingress can show up on a window sill, it’s possible that water is coming in from a hole in the roof and leaking down through the floorboards and the walls. You might need to head on up to the attic to find the source of a leak.

You’ll need a partner for this. While one of you sprays down the roof with a garden hose, the other should be inside the attic looking for the ingress point. The person operating the hose should start at the eaves, and work their way up the roofline.

Assess the Plumbing

Leaks often originate in old, worn pipes and plumbing fixtures, and most will start either in the shower pan or the toilet seal. Curled or warped flooring, loose tiles, and discoloration indicate a leak is originating around one of the bathroom fixtures. If you don’t fix a bathroom leak asap, water will rot the subfloor, and you’ll have to replace all of the bathroom floorings, which can be an extensive and costly project.

There are a few ways to check if a toilet or shower pan is leaking. You’ll need to fill an eyedropper or syringe with dyed water, and inject it into the toilet bowl. If you find colored water on the floor, the seal is leaking and will need to be replaced. For the shower pan, you can inject the dyed water around the junction between the shower floor and the shower wall to see if water is getting sucked down into tiny cracks or holes.

Check the Gutters

Broken, worn gutters are usually the cause of a moldy or damp basement wall. If you’re getting evidence of water damage in the basement, go outside and look at the gutters on the side of the house where the basement is getting wet. Thoroughly inspect the drains, and use the garden hose trick again to find any cracks or tears in the gutters and downspouts. Continuous water damage to the basement wall can cause foundation issues in the long run, and make mold, cockroaches, and other pests thrive.

Test Windows and Doors

You might have warping or staining beneath a window or around the exterior door thresholds. Stand inside with the windows and doors closed where you suspect the water is coming in. Have your partner turn on the garden hose, and look for leaks. If water is coming in through the windows and doors, you’ll need to re-caulk them or possibly even replace them if the damage is extensive and has caused warping.


HVAC systems can cause a lot of condensation, which drips and pools and can damage your house. Rotting jambs around the tops and sides of the windows can be a sign of poorly insulated HVAC ductwork.

Dry Rot

Porch roofs that buttress up against the side of the house are a prime spot for water leaks and damage. The caulking gets old and may rot, and fail to protect the rest of the roof and the porch. If you notice mold on the porch and a sagging ceiling, water is most likely coming in because the caulking has worn away and rotted out. You can recaulk the area where the roof meets the side of the house, but waiting too long to fix this leak can mean a costly porch roof replacement down the road.

Outdoor Water Leak

An outdoor leak can be difficult to detect, but failing to find and fix an outdoor pool or sprinkler system leak can waste thousands of gallons of water per year and run up your water bill.

If you have a sprinkler or irrigation system, extremely lush, green areas of the lawn are indicative of a leak. To test the pool for a leak, put a bucket down on one of the pool steps, and fill it with water to match the pool’s water line. Mark the water levels on the inside and the outside of the bucket. Wait for at least 24 hours before checking the water levels. If there’s a mismatch, the pool is leaking.

Although finding the source of a water leak isn’t always easy, fixing it is usually beyond the scope of the average homeowner’s purview.  Contact an experienced and reputable plumber or handyman once you’ve found the source of a leak.

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