What Causes A Leak Under Kitchen Sink & How To Fix?

A leak under your kitchen sink unnecessarily increases your water use and runs up your utility bills. Apart from that, kitchen sink leaks often create a mess that you probably don’t want to deal with and can damage other areas of the kitchen sink. Before you fix the issue, you first need to know what might be causing the leak. Here are steps to find leaks under your kitchen sink and where to look to fix it. 

Check The P-Trap 

The p-trap is a piece of sink pipe equipment designed to stop foul smells in the pipe getting out into the air. You won’t always be able to see the p-trap, which can make things complicated.

The area can get clogged with debris over time, affecting the efficiency of the sink in draining the water. If that happens, a leak can happen sooner than you expect.

Fixing a clogged p-trap in your pipe isn’t too tricky. To fix it, all you need to do is flush the debris out of the area by using either a drain cleaner or a kitchen drain snake. The only exception is if the fixture gets damaged or worn out. In that case, you need to replace the entire unit.

Another often overlooked area that can cause leaks under your kitchen sink near the p-trap is the flanged tailpiece. This part connects the drain to the p-trap and is located under the strainer. Plumbing issues can arise if the tailpiece is improperly installed. The same problem occurs when the tailpiece cracks or wears out.

Assess The Faucet Seal 

The faucet-to-sink seal is placed at the point where the faucet and sink meet. You might also know this part as the faucet mount.

A loose faucet mount or seal is a common cause of a faucet leaks. The seal ensures that water splashed around the faucet doesn't trickle down. If the seal wears out, you'll often find water dripping into the sink cabinet.

You can lie down under the cabinet and observe to determine if the leak is coming from the faucet area. You should also check if the seal is still in good condition before doing anything. That way, you can decide if the seal needs to be tightened or replaced.

Investigate The Washer 

The washer is a small rubber part that looks like a disk and fits inside the faucet. It provides a tight seal in your kitchen faucet and prevents any leaks.

However, it’s common for washers to wear out since you actually use them quite often. This is partly because of the washer pressing against the valve seat each time you turn on the faucet.

The friction eventually leads to rapid wear-and-tear on washers, which can lead to a leak under the kitchen sink. A common sign of a worn-out washer is constant dripping around the spout. If a worn washer causes leaking, there isn’t any other choice than to buy a new unit and replace it the old one to fix the leak.

Examine The Faucet 

Once you notice leaks under the kitchen sink, check if the faucet is still functioning properly. Sometimes kitchen faucets leak because of defective parts or age-related wear and tear.

If your faucet is bad, you might notice water dripping from under the base or in other cases barely any water coming out of it. Another common symptom of defective faucets is standing water pooling on your sink's surface.

You may contact a professional plumber to examine the faucet to see what's causing the problem. You can inspect the unit yourself—a damaged washer or gaskets are common culprits.

You should also examine the faucet aerator. It is possible to damage the aerator's seal while cleaning the aerator. That often results in water running down the spout and trickling into the cabinet when the faucet runs.

If you have a sprayer attached to your leaky sink, inspect the hoses in your kitchen sink for holes. You want to check other surfaces for any cracks or damage that can cause future plumbing issues.

Check The Valve Seat & O-ring

The valve seat connects the spout and faucet and is integral to the compression mechanism. So, checking the valve seat is always a good idea when you run into leaking issues.

Water accumulates at the valve seat, which makes corrosion inevitable. If the corroded valve seat continues to rust, you can get a severe leak on your hands in no time. The best way to avoid this problem is to clean the part yourself or include it in your routine plumbing service.

The O-ring is made of rubber and helps shift water around by creating a seal and helps your faucet remain in position. The O-ring eventually wears out from repeated use, as is common with most sink parts.

The most noticeable downside of a worn-out O-ring is frequent water leaks around the faucet handle. You will need to replace the O-ring if you notice a leak around that area.

Inspect The Water Supply Lines 

The water supply lines provide the water needed for all your kitchen uses — ranging from cooking, washing, and more. Most standard sinks have two water supply connections, but some can have more.

If you notice any excess moisture or leaks making it into your kitchen cabinet, take a look at your water supply lines. Any of those lines can have a crack that lets water drip under the sink.

In other cases, you can trace the problem to a defective gasket or a loose connection in the water supply lines. Check the pipes properly to pinpoint the exact cause and fix things.

Look At The Drain 

If other parts of the sink check out, the next place to inspect is the drain. Plumbers often seal the drain with plumbers tape or putty to stop water from seeping through. 

But putty dries over time, which reduces its effectiveness, and the same thing occurs to plumbers tape. This can create the perfect conditions for a drain leak to develop.

One specific place to look in the drain is the basket strainer. The basket strainer keeps foreign matter from your kitchen sink with its mesh screen. The problem with this equipment is that it can also wear out and start leaking. To confirm, fill the sink with water and inspect the sink-to-basket gaskets from underneath the counter. 

In addition, the kitchen drain can also suffer from age-related wear. In this case, you will need to replace the entire drain to stop a possible drain leak.

About the author 

Ryan Thompson is a residential and commercial plumber from Miami, Florida. He has over 20+ years of plumbing experience. He is also a huge DIY enthusiast who does all types of improvement projects around the house.