Leak Under the Kitchen Sink? Here’s How to Fix it

By: Diana Rodriguez-Zaba
Updated on: October 9, 2023

Puddles under your sink? Is water seeping under your kitchen floorboards? The annoying drip, drip, drip of water?

There’s no doubt about it – a leaking kitchen sink can be a frustrating process. And unless you repair it quickly, your leaky sink can cause water damage that spreads throughout your kitchen.

Fortunately, it is possible to fix leaks in your kitchen sink in a few simple steps. As one of Chicago’s leading water damage restoration companies, we’ve seen many leaking kitchen sinks (and the water damage), and we know how to fix these frustrating issues. 

In this blog, we’ll walk you through the process of finding a leak, addressing the cause (whether you’ve got a sink leaking underneath or a kitchen sink leaking around the edges), and repairing the problem.

Let’s dive in. 

Why is My Kitchen Sink Leaking Underneath? 7 Common Causes

kitchen sink leaking underneath

Many things can cause a kitchen sink to leak. Here are a few of the most common causes:

1. A corroded valve

Your kitchen sink uses a series of valves to control water flow and keep pipes from leaking. When those valves corrode or break down, though, it compromises the seal. 

One of the most critical valves is the valve seat, which connects the kitchen faucet and spout. When this valve starts to break down, it will cause leaks and pooling water.

2. A damaged O-ring

The O-ring is a small disk that, together with a few screws, holds your faucet handle in place. Over time, O-rings wear out or loosen with use, and when they do, the faucet will start leaking around the handle. 

3. Worn gaskets or washers

Does your faucet leak when you turn it on? If so, the problem could be failed washers or worn-out gaskets. 

Most faucet leaks manifest as puddles on top of your sink when the faucet is turned on, but some leaks go under the countertop and drip beneath the sink, so be sure to look under the basin for leaks, as well.

4. A backed-up p-trap

The p-trap is the curved pipe that sits below your sink. It moves wastewater away from the sink. The pipe’s unique curve prevents sewer gas from wafting back up your plumbing and into your kitchen. 

While the curve in the pipe serves an important purpose, it’s also vulnerable to clogs and leaks. If gunk or pieces of food build up in the p-trap, it can block the flow of water and cause the sink to overflow

5. Old drain putty

The plumber who installed your kitchen sink likely sealed the drain with putty to prevent leaks. Over time, that putty can thin or start to dry out, and when it does, the drain can develop a leak. 

6. High water pressure

While high water pressure sounds good, it can be tough on your pipes. For most homes, the ideal water pressure is between 40-60 PSI

Water pressure that is higher than that puts excess strain on pipes and can cause breaks and bursts in your plumbing – especially under your kitchen sink. 

7. Loose water supply connections

If you’ve noticed a constant leak under your sink, the problem is likely your water supply. Most sinks have two water supply lines – a hot and cold water line.

These lines are vulnerable to leaks, especially if their connections become loose or corroded. In extreme cases, a leak in these components can flood your kitchen

How to Find the Source of a Leak Under the Kitchen Sink

source of leak in kitchen sink

Before you can fix a leak in your kitchen sink, you’ve got to identify the source. Here’s how to pinpoint where the leak is coming from:

Conduct a “flow test”

If water is pooling or dripping under your sink, use a dry rag to wipe up the water and dry everything beneath your sink, including the garbage disposal, durian pipes, water lines, and shut-off valves. 

Next, you’re going to look at your sink’s drain pipes. Do this by running water into both sink basins (if yours is a dual sink), one basin at a time. Allow the water to run for 2-3 minutes while you inspect the underside of the sink for leaks with a flashlight or a dry tissue.

Start inspecting for leaks where the pipes meet the sink basin. Move down your plumbing gradually, using the flashlight to spot any leaks or drips.

Conduct a “basin test”

If you couldn’t find a leak during the flow test, move on to the basin test. To conduct this test, put a plug in your sink’s drain and fill the basin with water. Once the sink is full, remove the plug simultaneously and allow the sink to drain. 

Next, turn on your garbage disposal. This process puts your pipes under significant stress and allows you to monitor for leaks. 

If you look under the sink and don’t see any water dripping or pooling, start the dishwasher and allow it to run for a few minutes, inspecting all the pies under your sink for leaks. 

Conduct a faucet stress test

If you haven’t identified a leak in the last two tests, move on to a faucet stress test. To conduct this test, look closely at your sink’s shut-off valves and supply lines. Pay special attention to any rust, corrosion, or mineral buildup on these critical components. 

Next, turn the faucet on and off, moving the spout back and forth. Turn on the sprayer (if you have one) and check for signs of moisture under the sink. If you still can’t identify the source of the leak, it’s time to call a plumber for a professional consultation. 

How to Fix a Leak Under the Kitchen Sink

Here are our top tips for fixing a leak under your kitchen sink:

Faucet leaks

Faucet leaks are generally easy to fix. In most cases, replacing the faucet with a new one will be enough to stop water from pooling or dripping when you turn the sink on. 

Leaks in the drain seal

If your sink leak is coming from the drain seal, follow these steps:

  1. Use a pair of pliers to remove the old drain seal.
  2. Apply new adhesive to the bare drain. Don’t apply too much – a thin coat is more than enough.
  3. Replace the seal, centering it around the drain.

Drain leaks

If the leak comes from the drain (and drips into the cabinet below), the problem is likely a loose nut. If tightening the nut doesn’t fix the problem, follow these steps:

  1. Look at the drain outlet flange and verify that plumber’s putty was used to seal the area
  2. Check the rubber gasket seal to make sure it is lying flat and flush
  3. If those steps don’t stop the leak, take the drain apart and look for damaged or cracked components. Replace anything that is worn out or corroded.

What to Do About Water Damage

kitchen water damage restoration

Left unattended, water damage can wreak havoc in your kitchen. Mold and mildew can form within just 24-48 hours of water damage, and when they do, they pose a series of health risks for you and your family.

To minimize the impact of water damage, you need to address it quickly. Here’s what to do:

  • Use dry towels or a mop to soak up any standing water under the sink. If the sink continues to leak, place a bucket or basin underneath it to catch drips and stop them from pooling on your wood cabinets
  • Use bleach and hot water to wipe the area down and stop mold growth in its tracks. Dry thoroughly. 
  • Promote airflow by leaving the cabinet open and placing a standing fan in front.

If you’ve had water damage under your sink, we recommend contacting a water damage restoration professional, like the team here at ServiceMaster Restoration by Zaba.

Even if the water damage seems insignificant, the kitchen sink could be leaking under the floor, which can lead to mold, mildew, and other damage where you can’t see it.

Restoration teams will clean up the mess, prevent or resolve mold growth, and leave your kitchen as good as new. 

How to Prevent Leaky Kitchen Sinks 

The easiest way to prevent leaking kitchen sinks is to perform regular maintenance. Inspect your kitchen sink for worn-out or corroded parts and replace them promptly.

Check your home’s water pressure, keep it within the ideal range, and avoid pouring grease or large chunks of food down your sink drain.

Dealing with Water Damage Caused by a Leaking Kitchen Sink in Chicago? We Can Help!

Don’t face water damage alone! Our team is here to help! Contact us today to learn more about our water damage repair and restoration services or request your repair quote.