The short answer
Check the Drain Assembly
Start by looking under the sink while the water runs. The drain assembly includes the basket strainer, the tailpiece, and the slip nuts that connect to the P-trap. A leak often appears at these threaded joints because the nuts loosen over time from vibration or from using a garbage disposal.
Tighten the slip nuts by hand, then with a wrench, but do not overdo it. If the leak persists, the rubber gasket inside the nut may be cracked or compressed. Replacing that small gasket is a simple fix. For a persistent leak around the strainer, the putty seal under the flange may need to be redone.
- Look for water drips on the pipes and the cabinet floor
- Feel the slip nuts for looseness
- Inspect the rubber gaskets for cracks or wear
- Check the putty seal around the basket strainer
- Run water and watch the joints while the sink drains
Inspect Supply Lines and Valves
The water supply lines that connect to the faucet can leak at the shutoff valves or at the compression fittings under the sink. These lines are often braided stainless steel, and the rubber washers inside can wear out. A small drip may appear only when the water is on, so turn the faucet on and off while you watch.
If you see water at the valve, tighten the packing nut slightly. If the leak is at the fitting, replace the washer or the entire supply line. Also check the shutoff valves themselves; they can develop leaks at the stem. If you live in Rockwall, keep your shutoff valve location written down for quick access in an emergency.
Look for Damage from the Disposal
A garbage disposal can cause a leak at the connection where it meets the sink drain. The rubber gasket that seals this joint can split, or the mounting ring can loosen. Run the disposal briefly with water to see if water sprays from that area. If it does, the gasket likely needs replacing.
Also check the dishwasher drain hose if it connects to the disposal or the sink drain. A loose clamp or a cracked hose can leak water when the dishwasher runs. Tighten the clamp or replace the hose if you see cracks. Catching these issues early prevents water from soaking the cabinet base.
When to Call the Pros
Some leaks are easy to fix yourself, but others signal a bigger problem. If the leak comes from inside the wall, or if you notice water staining on the cabinet or floor, the issue may be a broken pipe behind the drywall. In that case, turn off the water and call local water damage pros to assess the situation.
Water that has already soaked into the wood cabinet or subfloor can lead to rot and mold. The pros use moisture meters and drying equipment to handle that kind of damage. If the leak has been going on for a while, you might see warped wood or a musty smell. Acting quickly reduces the risk of further damage.
- Water stains on the cabinet or floor
- Musty odor under the sink
- Leak that continues after you tighten the fittings
- Water dripping from the wall or ceiling below
- Faucet base leaks at the countertop
Prevent Future Leaks
Regular checks can catch small problems before they become big ones. Once a month, run water under the sink and inspect all the connections. Look for any signs of dampness, corrosion, or mineral buildup on the pipes. Tighten loose nuts as part of your routine.
Avoid storing heavy items against the pipes, which can stress the joints. If you have a garbage disposal, use it properly and avoid overloading it. Replacing worn gaskets and washers as soon as you notice a drip is cheaper than dealing with water damage. For peace of mind, you can also have a water damage inspection done periodically.
Water damage does not wait
Water keeps spreading into floors and walls, so it is worth acting early. Calls are answered 24/7.
Call Now (469) 698-4610Frequently asked questions
Why does my sink leak only when I run the water?
That usually means the leak is in the supply lines or the faucet itself, not the drain. Turn the water on and watch under the sink. Check the compression fittings and the shutoff valves. A worn washer or loose nut is often the culprit.
Can a small leak under the sink cause mold?
Yes, even a slow drip can keep wood and drywall damp, which encourages mold growth. If you notice a musty smell or dark spots, you may need mold remediation. Dry the area thoroughly and fix the leak quickly. If mold has spread, consult a mold professional.
What should I do if the leak is from the pipe in the wall?
Turn off the water supply at the main shutoff valve right away. That kind of leak may require opening the wall. Call the pros to assess the damage and find the source. They can also dry out the wall cavity to prevent mold.