kitchen sink leak

The Most Common Causes of Kitchen Sink Leaks

It’s happened to almost everyone whose home is more than 15 years old:  You go under the kitchen sink to get something you haven’t needed for a long while and you notice a weird odor.  Or maybe a dark stain on the cabinet floor.  Or a container that has water in it when it should not.  

Did you spill something?  Did the cat knock over the detergent or something?

Wait a minute—what if something is leaking under there?  The primary cause of cabinet failure is undetected leaks under the sink.  So it’s a good idea to check once in a while and call your local plumber if you detect moisture of any kind.

Of course, if you are able, you can do your own inspection under the sink to see what’s going on.  And if you are mechanically inclined, you may be able to make a repair on your own.

It’s helpful, too, to check the common sites for leaks to make sure you’ve covered all your bases.  After all, just because you found one leak source doesn’t mean there can’t be another.

Find source of water leak:

Here’s a helpful list of what to check out when you are searching for the source of the leak.

First, just get a flashlight and take a few minutes to look around in the cabinet.  Is there any water dripping now or does it look like the water must have shown up in the past?  Start from the bottom shelf of the cabinet and work your way up. If you spot a puddle look directly above it being careful to inspect all items as you proceed vertically.  Check for drips coming from hoses, water supply lines and drain lines and/or appurtenances directly above the puddle.  

If you have no puddle or wet spot, just start working your way up with your light while checking everything below the sink until you spot some water.  Don’t forget to look around the edge of the sink also.

If you don’t spot any water then slowly touch every pipe and connection under the sink, one at a time, starting from the top down. 

Look at your fingers after each item is touched to see if there is water present.  If you still don’t find the water source, turn on the faucet and check all the items again.

Finally, if no water is found, then fill up the sink to the top and then release the water.  Look at all the drain lines for a presence of water.

Cause of leaks under kitchen sinks (in no particular order):

Loose faucet or bad faucet-to-sink seal:  If the faucet mounts are loose or the seal under the faucet is compromised then whenever water is splashed on the top of the sink around the faucet, it will leak down into the cabinet.

Defective faucet:  Faucets can develop internal leaks due to age, defect and cracking or failure of parts.  When this happens water will drip out of the faucet base into the sink cabinet.

Loose faucet aerator:  Sometimes if the spout aerator is cleaned or replaced, the seal or aerator itself can be compromised and water will actually run down the inside of the faucet spout and show up in the cabinet every time the faucet is operated.

Loose or defective sprayer:  The side spray (if equipped) is always pressurized on kitchen faucets when the faucet is on, even though you may not be using it.  Check the hoses and all surfaces for cracks and leaks.

Water supply lines:  Check both ends with water on.

Under sink valves:  Valves can start leaking at any time and especially right after they are used.  

Basket strainers:  Cheapot Depot type basket strainers are prone to loosening up and leaking.  Check the sink-to-basket gaskets with the sink full of water.

Drain flanged tailpiece:  Located under the basket strainer this is a common source of leaking when it cracks or is improperly installed.

Continuous waste tubular piping:  As with flange tailpieces this assembly can crack, rot out, or be installed improperly.

Tubular P-Traps:  Configured with slip nuts these parts are subject to the same problems as the Continuous waste.

Trap adapter:  Connects tubular parts above to the solid waste lines.

Drain line:  Metal drain lines can rot out and plastic can pull apart or crack. 

Water lines:  Copper,  plastic or galvanized water lines can wear out and corrode.

Garbage Disposer:  When the garbage disposer is the source of the leak it can be internal or external leakage.  Determine which one is causing your problem and replace the right item.


As we can see, there are many parts to the plumbing system connected to the kitchen sink.  As long as we are methodical about our approach to finding the leaks we will be able to identify the correct problem(s) every time.

If you are unable (or unmotivated) to do this and need help with any of your plumbing systems, please give us a call. 

We are State licensed to serve all of Northwest Indiana as well as the south suburbs in Illinois.  Phones are answered by live operators 24 hours a day.