Discovering a constant leak under your kitchen sink can be frustrating and potentially damaging to your home. Water pooling in your cabinet not only causes unpleasant odors and mold growth but also risks structural damage to your flooring and cabinetry. Fortunately, understanding the most common causes of these leaks can help you fix the issue quickly—or know when to call a plumber.
Common Causes of Kitchen Sink Leaks
Several components underneath your kitchen sink can be responsible for a constant leak. Identifying the exact source is the first step toward solving the problem.
1. Faulty or Worn-Out Pipe Connections
Over time, the connections between your pipes can become loose or degraded, especially in areas where water flow is frequent or high-pressure.
- Pipe joints may loosen due to vibrations or repeated use.
- Compression fittings can dry out or crack.
- PVC connections may be improperly glued or sealed.
If the leak stops when you don’t use the sink, it’s likely a connection issue rather than a supply line or drain problem.
2. Leaking Drain Pipes
Drain pipe leaks are common because they handle a high volume of wastewater and can clog or degrade.
- P-traps may crack or come loose.
- Washers inside drain connections may become brittle over time.
- Clogs can cause backflow pressure, forcing water out of weak spots.
Leaks from the drain often occur only when the sink is draining water, not while it’s off.
3. Damaged Faucet or Sink Components
The faucet base, sprayer hose, or sink basin itself can all be potential sources of a leak. Faucets and sinks endure daily use and can develop minor cracks or worn seals.
- Faucet O-rings may crack, allowing water to seep into the cabinet.
- Pull-out spray hoses can degrade, especially where they connect underneath.
- Cracks or chips in the sink basin may allow water to escape through the countertop.
If the leak starts as soon as you turn on the faucet, one of these components is likely the culprit.
Diagnosing the Problem
It’s important to determine the source of the leak before attempting a repair. Here’s how to troubleshoot:
Step 1: Dry and Inspect
Use a towel to thoroughly dry all the pipes and surfaces under the sink. Then run the water and observe carefully to identify where moisture reappears.
Step 2: Check Supply Lines
Inspect the hot and cold water supply lines that run from the wall to the faucet.
- Feel the connections to see if they are damp.
- Look for signs of rust, mineral buildup, or water dripping down the lines.
- Wiggle the fittings to see if movement causes leaking.
Step 3: Examine the Drain Assembly
Run water down the sink and watch the drainpipe closely.
- Check around the P-trap and any pipe joints for drips.
- Watch for slow-forming leaks, which may take a minute or two to appear.
- Feel underneath the sink for hidden moisture.
Preventing Mold and Water Damage
Even a small leak can cause major issues over time if not addressed. Mold thrives in dark, damp places, and the cabinet under your sink is the perfect environment.
Warning Signs of Mold and Damage
- Musty odors
- Warped or discolored cabinet base
- Visible mold on surfaces or walls
- Pest infestations (some insects are attracted to moisture)
Protective Measures
- Place a plastic tray or waterproof mat under the sink to catch minor leaks.
- Keep the area dry and well-ventilated.
- Use caulk to seal any visible gaps around pipe entry points.
Tools and Supplies You May Need
Before attempting a repair, gather the right tools and materials. In many cases, you can handle minor fixes yourself.
Here’s a paragraph with bullet points for the tools you might need:
To fix a typical leak under your kitchen sink, it’s useful to have the following on hand:
- Adjustable wrench for tightening pipe fittings
- Pipe tape (Teflon tape) to reseal threaded connections
- Plumber’s putty to seal around drain flanges
- Bucket or bowl to catch water during the repair
- Replacement washers or O-rings in case seals are worn
- PVC pipe and couplings if a section of the drain needs to be replaced
- Flashlight to help inspect hard-to-see areas under the sink
Having these supplies nearby will make it easier to handle repairs immediately and prevent further damage.
When to Call a Professional Plumber
While many kitchen sink leaks are DIY-friendly, there are times when you should bring in a licensed plumber. Knowing when to seek help can save time and prevent bigger problems.
Call a Plumber If:
- You see signs of mold or structural damage.
- The leak is coming from a cracked sink or countertop.
- Pipes are corroded or difficult to access.
- Temporary fixes keep failing.
- The leak is affecting walls or floors beyond the cabinet.
Professional plumbers have the tools and experience to diagnose complex leaks, replace faulty components, and ensure your plumbing is up to code.
Final Thoughts
A constant leak under your kitchen sink can lead to bigger headaches if left unchecked. Fortunately, most leaks come from common sources like loose fittings, cracked drainpipes, or worn-out gaskets. With some basic tools and attention, you can often stop the leak yourself. But if you spot signs of mold, water damage, or ongoing issues, don’t hesitate to call a professional. Addressing leaks promptly not only protects your kitchen but also helps you avoid costly repairs in the future.
