Leak Under the Kitchen Sink: Common Causes and What to Do Next

You open the cabinet to grab a cleaning spray and notice a damp spot, a puddle, or a musty smell. A leak under the kitchen sink is a common household surprise, and it's worth taking seriously even when it looks small.

Some leaks come from the plumbing. Others come from the sink itself or the way it's attached. Knowing the difference helps you decide what to do next.

What to Do Right Away

If water is actively leaking, take these simple steps:

• Place a bucket or towels under the leak to catch water
• Shut off the water supply to the sink, if you can do so easily, using the valves beneath the sink
• Remove items from the cabinet so they don't get damaged
• Avoid using the sink until the source is found
• Contact a professional if you can't tell where it's coming from

Please don't take apart plumbing you're unfamiliar with. Small mistakes can turn a manageable leak into a larger one.

Common Sources of Leaks

Supply Lines and Shutoff Valves

The flexible lines that carry water to the faucet, and the valves that control them, can loosen or wear out. Leaks here often drip in one spot or appear when the water is running.

Faucet Connections

Water can seep from beneath the faucet base, down the inside of the cabinet, and look like a plumbing leak even though it started at the countertop.

Drain and Trap Connections

The drain basket, tailpiece, and trap are connected with fittings that can loosen or wear. Leaks here often appear when the sink is filled and drained.

Garbage Disposal

Disposal leaks can come from the sink flange, the connections, or the unit itself.

The Sink Itself

Cracks in the basin or failure of the seal between the sink and countertop can let water reach the cabinet. Signs include leaks that show up only when the sink is used heavily, water around the rim, or damage along the countertop's edge.

Why Leaks Matter

Moisture in a sink cabinet can:

• Swell and weaken the cabinet floor
• Stain or damage the underside of the countertop
• Encourage mold and musty odors
• Corrode fittings and brackets
• Loosen the sink's support and sealant

Small leaks are easiest to fix early.

When the Sink May Be the Problem

Consider the sink itself if:

• Water appears around the rim or the seam with the countertop
• The sink has visible cracks or a failing seal
• The sink is loose or has shifted
• Leaks come back after plumbing connections have been repaired
• The sink is old, and multiple issues appear around the same time

If an undermount sink has become detached from its support, restrapping may help. In other cases, replacement is more dependable, especially when the sink is cracked or corroded.

Why It Helps to Have a Specialist Take a Look

A leak might have more than one source, and repairs that treat only one may not solve the problem. A specialist who understands sinks and countertops can assess the sink, its mounting, the seal, and the plumbing connected to it.

How to Help Your Specialist Diagnose a Leak

You can make a leak much easier to trace with a few careful observations. Note when the leak happens: only when the faucet runs, only when the sink drains, only when the dishwasher is going, or all the time. Take photos of any wet spots, stains, or corrosion.

Dry the area thoroughly, then place dry paper towels under different parts of the plumbing. Checking them later can show which connection is dripping. This is an easy, safe way to narrow things down without taking anything apart.

Clear the cabinet, protect the floor, and keep the area accessible for the visit. Avoid tightening fittings or applying sealants on your own, because that can hide the real source or cause new leaks. The more information you can share, the faster a professional can figure out whether the problem is a supply line, a drain connection, the faucet, the disposal, or the sink itself.

How I Hate My Sink Can Help

I Hate My Sink specializes in kitchen sink replacement and also offers sink restrapping, sink and countertop repairs, faucet installation, and garbage disposal installation. Depending on the existing sink, countertop, dimensions, and installation requirements, a sink may be replaced while keeping the existing countertop. Our approach is one sink, one day, no kitchen demolition.

Your free estimate begins with an in-person evaluation. We've replaced more than 3,500 sinks and stand behind our work with a 100% customer satisfaction guarantee.

Frequently Asked Questions

Why is water leaking under my kitchen sink?

Common causes include loose supply lines, worn drain fittings, faucet leaks, disposal issues, or a failing sink seal or crack.

Is a leaking kitchen sink an emergency?

An active leak should be addressed promptly. Shut off the water to the sink if you can and contact a professional.

Can a sink leak around the rim?

Yes. If the seal between the sink and the countertop fails, water can seep into the cabinet below or under the countertop's edge.

Does a leak mean I need a new sink?

Not always. Many leaks come from plumbing connections. A specialist can identify the true source.

How do I know whether restrapping or replacement is better?

It depends on the sink's condition and support. An evaluation will help you decide.

Dealing With a Leaky Sink?

If you suspect your sink is the source of the leak, I Hate My Sink can evaluate your existing setup and help determine the right solution.

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