A leak under kitchen sink can come from a pressurised supply hose, a faucet connection, the drain, or an appliance connection. The first wet spot is more useful than the puddle: water can run along a pipe or cabinet surface before it drips. Empty the cupboard, dry the area and check where moisture returns, testing the tap and drain separately. If water is flowing steadily, close the under-sink shutoff valve if it operates normally. Don’t force a stuck valve or touch wet electrical parts. Promptly tracing and stopping the leak can limit damage; call a plumber if you can’t identify the source or the leak continues.
Start by protecting the cupboard and checking whether the leak is active. Move stored items away from the wet area, place a container beneath a drip and use towels to remove standing water. If the cabinet floor is soaked, dry it as thoroughly as you can and leave the doors open to help air circulate. Keep an eye out for swelling, peeling surfaces, a musty smell or water that reappears after drying.
If water is coming from a supply hose or valve, it may continue even when the tap is off. Close the relevant shutoff valve beneath the sink gently, following the valve’s design. If it will not turn easily, appears damaged, or continues to leak, don’t force it. Use the home’s main water shutoff if you know how to operate it safely, and arrange plumbing help.
Water near a waste-disposal unit, dishwasher connection, outlet or plug calls for extra care. Don’t operate or handle electrical equipment while the area is wet. If water is near electrical fittings, keep clear and seek appropriate help rather than reaching into the cabinet.
Look above the puddle as well as around it. Water can travel along the underside of a sink, a hose or the cabinet wall, so the place where it collects may be some distance from the fault. A dry paper towel pressed gently against fittings can help reveal a small drip. Avoid placing your hand near moving or electrical parts.
| Possible source | When water may appear | What to inspect | What the pattern suggests |
|---|---|---|---|
| Supply hose or shutoff valve | It may leak even when the tap is off | Hose ends, valve body and nearby pipework | A wet fitting or hose suggests a pressurised supply leak |
| Faucet connections or base | Often during or after using the tap | Connections beneath the faucet and the area around its base | Water can run down from the sink top or a connection; trace it to the highest wet point |
| Drain, trap or waste connection | Usually while water is draining | Drain outlet, joints and the curved trap beneath the sink | A joint may leak when waste water passes through it |
| Dishwasher or disposal connection | May occur while the appliance runs or drains | Visible hose connections and the disposal body or inlet | A leak linked to an appliance cycle narrows the search, but don’t run it if the area is wet near electrical parts |
| Condensation or a spill | May appear without an obvious drip from a fitting | Cold surfaces, the sink underside and stored containers | Dry everything and see whether moisture returns at a specific point |
These patterns are clues rather than proof. For example, a supply connection can leak more noticeably when the faucet is running, and water from a faucet base can travel underneath the sink. Test one part of the system at a time so you can connect the leak to an action.
A useful clue is whether the water appears with the tap off, while water is flowing, or only as the sink drains. That timing helps distinguish a supply-side problem from a waste-side problem, but it doesn’t identify the faulty part on its own. Record what you observed; the detail can help a plumber narrow the diagnosis.
A small, accessible issue may be manageable for someone comfortable with basic plumbing, but the repair depends on the source and fitting. A loose-looking connection is not automatically safe to tighten: excessive force can damage a fitting, and tightening the wrong kind of joint may not stop the leak. Follow the instructions for the specific fixture or part, and shut off the water before working on a pressurised supply connection.
A plumber can identify whether the repair involves a supply line, faucet, drain fitting or appliance connection and explain what needs to be replaced or adjusted. The likely cost depends on the fault, access, parts and any damage that has already occurred, so ask what the diagnosis and proposed work cover before authorising a repair. Water-damaged cabinet material may also need attention beyond fixing the plumbing source.
Once the leak is stopped or isolated, remove wet items and dry the cabinet surfaces. Keep the area accessible so you can see whether moisture returns. Don’t cover a damp patch with stored goods or assume that a dry-looking surface means the leak is fixed; check again after the relevant fixture or appliance has been used, if it is safe to do so.
A temporary container can catch a slow drip, but it is not a repair. Check it regularly and don’t leave an active leak unattended. Avoid smearing sealant over a wet joint or applying a patch without confirming the source: that can obscure the fault and make a proper repair harder.
If the leak continues after an attempted repair, stop using the affected fixture or appliance where practical and shut off its water supply if you can do so safely. A persistent leak under the kitchen sink warrants professional diagnosis, particularly when water is emerging from behind the cabinet, a wall or a hard-to-reach connection.
A supply hose or shutoff valve can leak while the faucet is off because those parts may remain under water pressure. Water left from an earlier use or condensation can also collect beneath the sink. Dry the area and check which surface becomes wet first.
Check whether moisture appears while the tap is off, while water is flowing, or as the sink drains. A drain leak often becomes visible when water passes through the waste fittings, while a supply leak may continue with the tap off. Timing is a clue, so inspect the actual point where water first appears.
That depends on the source and whether you can contain the water. If the leak is active, worsening or close to electrical equipment, stop using the sink and isolate the water if safe. Don’t rely on a container as a long-term solution.
Only consider it if you have identified the connection, can shut off the water where needed and understand the fitting. Over-tightening or working on the wrong joint can cause damage, and a leaking valve or damaged hose may need replacement rather than tightening. Call a plumber if you are uncertain.
Call if you can’t locate the source, the leak persists after a repair, a valve will not close, or water is flowing steadily. A plumber is also the safer choice for hidden pipework, damaged supply lines and leaks near electrical equipment.
For a leak under the kitchen sink, trace the first wet point rather than assuming the drain is at fault. Dry the area, test the faucet and waste system separately, and shut off water if a supply leak is active. If the source is unclear or the drip returns, arrange a plumber’s inspection before cabinet damage spreads.
