The short answer
Common Leak Sources Under the Sink
The water supply lines, which are the flexible hoses connecting your faucet to the shutoff valves, often develop leaks. Their rubber washers can wear out, or the connections can become loose over time. A steady drip from these lines is a frequent culprit, especially if you notice water pooling directly below the faucet handles or valves. Tightening the connections or replacing the lines usually stops this leak.
The drain assembly is another major source of leaks. The large rubber gasket that seals the sink strainer to the sink bowl can crack. Water then leaks down the outside of the drain pipe instead of flowing through it. You might see water dripping from the metal flange of the strainer itself. Replacing this gasket, often called a sink flange gasket, requires removing the strainer basket from above.
- Loose or cracked water supply line connections
- Worn-out sink strainer basket gasket (flange gasket)
- Failed garbage disposal mounting gasket or hose connection
- Cracked or loose slip-joint nuts on the P-trap
- Corroded or damaged P-trap pipe section
- Deteriorated plumber's putty under the sink basket
How to Find the Exact Leak Location
Start by drying everything under the cabinet completely with an old towel. Place a dry paper towel or cardboard on the cabinet floor to catch drips. Then, run the water in the sink normally, using both the hot and cold taps. Watch the paper towel for the first signs of moisture to pinpoint the general area where the leak starts. This simple test often reveals the leak's origin quickly.
Immediate Steps to Prevent Water Damage
Your first action should be to turn off the water supply. Locate the small shutoff valves on the wall under the sink and turn them clockwise until they stop. If those valves are stuck or missing, you may need to shut off the main water supply to your home. Place a bucket under the leak to catch any remaining drips and remove all items from the cabinet to keep them dry.
When to Call a Professional Plumber
Call a plumber if you cannot locate the leak source, if the shutoff valves are corroded and won't turn, or if the leak is from a pipe you cannot easily access. A significant leak from a supply line inside the wall also requires a professional. If you are not comfortable making repairs yourself, hiring a plumber ensures the fix is done correctly and prevents a recurring problem.
Complex issues like a leaking garbage disposal seal or a corroded pipe that needs replacement are also good reasons to call a pro. They have the tools and parts to make a lasting repair. Attempting a complex fix without the right experience can sometimes worsen the leak or cause new problems. A plumber can also check your entire under-sink plumbing for other potential weak spots.
Addressing Water Damage from the Leak
Even a small, slow leak can cause significant damage over time. Water can warp the wooden cabinet floor and walls, causing them to swell or soften. It can also damage the subfloor beneath the cabinet. If the leak has been ongoing, you may notice discoloration, a musty smell, or even soft spots in the wood. These are signs that moisture has been absorbed deeply into the materials.
For any damage beyond surface moisture, contacting local water damage pros is a smart step. They have equipment to properly dry out the cabinet structure and subfloor, which is critical to preventing mold. They can assess whether materials need to be repaired or replaced. Leaving damp wood to dry on its own in a dark cabinet often leads to mold growth, which creates a bigger issue.
- Warped or swollen cabinet floor and side panels
- Soft, spongy feeling when pressing on cabinet wood
- Discoloration or dark water stains on surfaces
- A persistent musty odor coming from the cabinet
- Visible mold growth on wood or drywall nearby
- Damage to the subfloor extending beyond the cabinet
Talk to someone now
Phones are answered 24/7 for Gaithersburg and nearby communities.
Call Now (301) 281-4960Frequently asked questions
Can a leaking sink cause mold?
Yes, a persistent leak creates constant dampness, which is ideal for mold growth. Mold can start growing on wet wood or drywall within 24 to 48 hours. If you see discoloration or smell mildew, mold may be present behind the cabinet. It is important to dry the area thoroughly and quickly to prevent this.
Is a leak under the sink an emergency?
It depends on the leak's severity. A slow drip is not an immediate emergency, but it should be fixed soon to prevent damage. A steady stream of water is an emergency; turn off the water supply immediately. Any leak that causes water to pool on the floor requires prompt action to protect your home's structure.
Will my homeowner's insurance cover the damage?
Coverage depends on the cause and your specific policy. Sudden, accidental leaks like a burst supply line are often covered. Damage from a long-term, gradual leak may not be. Policies vary, and your insurer decides what is covered. You should review your policy and document the damage with photos for your claim.