The cabinet under a kitchen sink holds a lot of plumbing in a small space: two supply lines with stop valves, the faucet connections, the drain basket, a trap, often a garbage disposal and a dishwasher drain hose. A slow drip can soak the cabinet floor for weeks before anyone notices a soft spot or a smell.
The first job is to empty the cabinet, dry everything with paper towels and watch. Water flows downhill, so the wettest spot is not always the source. Run water in short bursts and look above where the drip lands.
Where the water is coming from
| Location | When it leaks | Common cause |
|---|---|---|
| Supply line or stop valve | All the time, even with the faucet off | Worn hose, loose nut or aging valve packing |
| Faucet base | Only while the faucet runs | Worn seals inside the faucet body |
| Sink drain basket | When the sink holds water | Failed putty or gasket under the basket |
| Trap and tailpiece | When water drains | Loose slip nuts or a cracked trap |
| Disposal | When running or draining | Worn seals or a cracked housing |
| Dishwasher hose | During dishwasher drain cycles | Loose clamp or cracked hose |
Stop the leak and narrow it down
- Close the stop valves.Turn the hot and cold valves under the sink clockwise. If the drip stops, the leak is on the supply side.
- Dry and wrap.Wrap a dry paper towel around each joint. The one that gets wet first is your source.
- Test the drain side.Fill the sink partway, then let it drain while watching the basket, tailpiece and trap.
- Check the disposal and dishwasher.Run each briefly with a flashlight on the connections.
Fix it yourself or call a plumber?
- IfA plastic slip nut on the trap is looseThenHand-tightening it is often enough. Do not overtighten plastic.
- IfA supply hose is bulging, kinked or corrodedThenReplace it soon. If the stop valve is stiff or leaking, have a plumber replace both.
- IfThe faucet leaks at the base or handleThenA cartridge or seal is usually worn. A plumber can repair or replace the faucet.
- IfThe disposal housing itself is leakingThenHousings usually cannot be repaired. Ask about replacement.
- IfThe cabinet floor is soft or stainedThenThe leak has been going for a while. Fix the source and let the cabinet dry fully before storing items.
Questions to ask the plumber
- Is the stop valve worth replacing while you are here?
- Can this faucet be repaired, or is replacement the better option?
- Is there any sign the leak has damaged the cabinet or wall?
- Will the dishwasher or disposal connections need adjusting?
Common questions
Why does the leak only show up when the dishwasher runs?
The dishwasher drains through a hose that connects under the sink, often at the disposal or a tailpiece. A loose clamp or cracked hose leaks only during the drain cycle.
Is a small drip under the sink urgent?
It is rarely an emergency, but it can damage the cabinet and invite mold. Close the stop valve if it is on the supply side and schedule a repair.
What drives the cost of a sink repair?
Which part failed, whether valves need replacing, the type of faucet, and how easy the space is to work in.
General information for Sunny Hills, not a quote or professional advice. In an emergency, call 911.