How Find the Source of Plumbing Leaks

by James Fitzgerald
Professional plumber doing renovation in kitchen home.

Plumbing leaks are incredibly common. They can result in high monthly water bills or water damage in your home. According to the Environmental Protection Agency, water leaks in an average household can waste almost 10,000 gallons of water every year, so it’s important to find and fix the source of the leak as quickly as possible.

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Fortunately, some leaks can be easily repaired, but others will require the aid of a professional plumber. But even if you do need to hire a plumber, finding the leak yourself can spare you the expense of having them track it down for you.

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How to Tell if You Have a Plumbing Leak

Monitor Your Water Bill

Most household water usage is fairly consistent month-to-month. If your water bill has spiked unexpectedly even though you haven’t been using more water than usual, it’s likely that you have a plumbing leak.

Watch Your Water Meter

Water meters are typically housed inside a box in the ground near the street in front of your home, but they’re sometimes located in back or side yards.

In the center of your water meter is a leak indicator dial, which is often an asterisk or colored triangle. You can use it to test for a leak by turning off all your water-using appliances (like your clothes and dishwasher) and fixtures (like your toilet, sinks and shower), then watching the leak indicator for several minutes to see if it moves. If it moves, you have a plumbing leak somewhere.

How to Find the Source of Plumbing Leaks

Now that you’ve determined you have a leak somewhere in your home, you’ll need to poke around the following areas to find the source.

Walls, Ceilings and Floors

If you see brown or yellowish water stains, bulging paint or black mold spots (especially in an area that’s not generally exposed to high moisture levels) on your walls or ceiling, that’s a strong indication that water is leaking behind them. Even if there are no visible signs of moisture damage or mold, a musky odor can mean that a leak has caused mold to form inside the walls or ceiling. Warped or spongy sections on your floor are a sign that the plumbing underneath your concrete foundation is leaking, which is commonly referred to as a “slab leak.”

You may be able to find the source of a leak in the ceiling by inspecting the plumbing lines in your attic, but a leak inside your walls or concrete slab will require the assistance of a professional plumber.


Inspect around the base of every water-supplied appliance (like your dishwasher, clothes washer, refrigerator and water heater) for puddles of water. If you find water, check for moisture along the entire length of the water supply line, at the connections on either side of the line, and the water supply valves (also called “shut-off valves”) on the wall. A supply line will usually leak because it’s cracked or damaged, so it will need to be replaced. Leaking connections are often loose and can be tightened down to fix the leak. A leaking shut-off valve can sometimes be fixed by tightening down its connections, but it will typically need to be replaced.

If the leak is coming from your water heater, also check for leaks at the pressure relief valve and replace it if it’s leaking. If the leak isn’t coming from the water supply line, connections, shut-off valve or pressure relief valve, the tank itself is probably leaking, and the water heater should be replaced as soon as possible. Even a small leak inside the tank can cause it to burst within weeks, which would end in a large flood inside your home.

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Kitchen and bathroom sinks can leak from the faucet, water supply lines and shut-off valves.

If a faucet is leaking, it’s usually from a bad valve stem or cartridge inside of the handle, depending on the type of faucet you have. Start by identifying which handle is causing the leak by turning off one of the water supply valves under the sink (either cold or hot) and see if that stops the leak. If not, shut off the other valve. The handle that corresponds to the shut-off valve that stopped the leak needs to be repaired with a faucet handle repair kit that matches your type and brand of faucet.

If it’s not the faucet that’s leaking, check for puddles of water, water stains, bubbling paint, mold or mildew inside the cabinets underneath your sink. If you spot any of those, look for moisture on the water supply line, the supply line connections and the shut-off valves. Tighten any loose connections and replace the damaged supply line or shut-off valve.


Toilets can leak externally at the water supply line or shut-off valve, or internally from a bad seal at the flapper — the rubber seal that separates the water in the tank from the bowl.

If there’s water on the floor surrounding your toilet, check for moisture on the water supply line, the supply line connections and the shut-off valves. Tighten any loose connections and replace the damaged supply line or shut-off valve.

If there isn’t any water on the floor, check for an internal leak by placing a few drops of food coloring into the bowl. If the flapper is leaking, you will see the food coloring in the toilet bowl within minutes. Check to ensure that the chain attached to the toilet handle isn’t obstructing the flapper and causing the leak. The next step would be to replace the flapper.


Wet and muddy spots or abnormally green patches of grass in your yard can mean that there’s a leak in an underground pipe, like an irrigation line or your home’s main water supply line. Carefully dig around the suspected area to uncover the pipe and find the leak. You may be able to repair an irrigation line yourself, but fixing a leak in the main water supply line will require a plumber.

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What to Do if You Find a Leak

While you may be able to fix a plumbing leak yourself, don’t hesitate to call a plumber if you’re not comfortable performing the repair. There are many cases where attempting the repair yourself can make the leak worse and cause even more expensive damage. You should also call a plumber if your water bill and water meter’s leak indicator show that you have a leak, but you can’t find where it’s coming from. In addition to finding and fixing the leak, a plumber will be able to check for damage that may have resulted from the leak, and they’ll help you take steps to prevent the leak from happening again.

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