Why is water leaking under my kitchen sink?
When the leak shows up tells you where it is. Water that appears with nothing running comes from the pressurised side: a shutoff valve or a supply line. Water only after the faucet runs points to the faucet's hose connections. Water only when the sink drains points to the trap, the strainer, a garbage disposal or the dishwasher hose.
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By Kasra Taheri, Founder, LoclisUpdated
Researched and drafted with AI, then checked claim by claim against the sources listed below before it was published. Prices and rules change; the dates beside each source say when it was last checked.
Step by step
Read when to stop and call a pro, further down this page, before you start.
Step 1: Clear and dry the cabinet
Empty the cabinet, wipe every pipe, valve and hose dry, and lay a dry paper towel on the cabinet floor.
Step 2: Wait with nothing running
Leave the sink and dishwasher off for an hour; a wet towel now points to a shutoff valve or supply line.
Step 3: Run the faucet only
Plug the sink so nothing goes down the drain, run hot and cold water for a minute, and watch the hose connections under the faucet and the spray hose.
Step 4: Fill and drain the sink
With the sink plugged and filled, wrap paper towels around each drain joint, then pull the plug and see which towel gets wet.[2]
Step 5: Check the disposal and dishwasher
Look at the dishwasher hose and clamp at the disposal, and at the disposal's discharge elbow and bottom plate.[2]
Step 6: Snug a leaking slip nut
If a trap nut drips, hand-tighten it and finish with a quarter-turn using pliers, snug but not overtightened.[5]
Step 7: Shut off a supply leak
If a supply line is leaking, turn its shutoff clockwise until it is tightly closed[3] before replacing the line; if the valve itself leaks or will not stop the water, use the main valve and call a plumber.
Step 8: Dry it out
Once the leak is fixed, leave the cabinet open with a fan on it so the wood dries within a day or two.[9]
Water under a kitchen sink almost always comes from one of a few joints you can see and reach: a shutoff valve, a supply line, the faucet's own hose connections, the drain trap, the sink strainer, a garbage disposal or the dishwasher hose. The fastest way to find which one is to notice when the water appears, then test each part of the plumbing on its own.
When the leak happens tells you where it is
Leaks with nothing running. That is the pressurised supply side, which holds water all the time. If a kitchen faucet leaks under the sink 24 hours a day, Moen points to three places: the home shut-off valves (angle stops), the house supply lines that lead to the faucet, and the faucet's own supply lines.[1]
Leaks only after the faucet runs. If the faucet leaks under the sink only after it has been used, Moen points to the cluster of faucet hose connections below the sink.[1] On a pull-down faucet, the spray hose and its connections move every time you use it, which makes them a common source.
Leaks only when the sink drains. That is the drain side: the trap, the tailpiece, the strainer where the drain meets the sink, or a disposal.
Leaks only when the dishwasher runs. That points to the dishwasher's drain hose where it joins the disposal or the sink drain.
Supply-side causes
A shutoff valve. Water around a valve's handle or stem usually means its seals are worn. Valves that are never turned can stiffen and leak when someone finally moves them: Oatey recommends exercising the valve handle annually by moving it between the open and closed positions a few times, which helps prevent mineral buildup inside the valve that can cause external leaks.[6] On a multi-turn valve, a slight drip at the stem can sometimes be stopped by gently snugging the packing nut just behind the handle. A valve that keeps leaking, or will not close, usually needs replacing.
A supply line. Look for a drip at either nut, or a bulge, kink or rust on the braided line. For a connection that drips, Oatey's advice is to tighten the nut by hand until it is watertight and, if it leaks, tighten the nut an additional quarter of a turn by hand.[6] A line that is split or bulging needs replacing.
The faucet's hose connections. Pull-down and pull-out faucets join several hoses under the sink with clips or quick-connects. A connector that is not fully clicked in, or a worn O-ring, drips while the faucet runs. Pressing the connector until it clicks, or replacing a worn O-ring, often stops the drip.
Drain-side causes
The trap. The curved pipe under the sink is held together by slip nuts, each pressing a washer against the pipe. If that washer has slipped, flattened or been put in backwards, the joint drips. Oatey's order of assembly: "The nut goes on first, followed by the washer, with the tapered side of the washer facing the fitting."[5] To snug a dripping nut, hand-tighten the nut, then finish with a quarter-turn using pliers, snug but not overtightened.[5] Go easy: "Excessive force can crack plastic fittings or strip threads, causing leaks."[5] Tape usually does not help here: slip-joint connections seal with washers, not thread tape.[5]
The strainer. The basket strainer that sits in the drain hole is sealed to the sink. "Plumber's putty is used to form a water tight seal between the sink and the faucet and between the sink and the drain."[4] When that putty dries out, water runs down the outside of the strainer body. That is fixed by resealing the strainer, not by tightening the trap below it.
The garbage disposal. To find a disposal leak, Moen's test is to plug the sink and fill it, wrap paper towels at the sink flange, the drain discharge elbow and the dishwasher connector, then release the stopper and check which towel is wet.[2] For the dishwasher hose, inspect the dishwasher connector or clamp for damage or deterioration and replace it if necessary, since they need to be tight.[2] Water dripping from the bottom of the disposal is a different problem: "If the drain discharge gasket is damaged, water can travel down in between the shell and the garbage disposal and drain out by the cover plate on the bottom."[2]
Water that is not a plumbing leak
Not every wet cabinet is a broken joint. Water splashing over the sink rim or around the faucet base can run under the countertop edge and drip into the cabinet. Cold supply pipes can also sweat in humid summer weather. Dry everything and watch: condensation shows up evenly along the cold pipe, while a leak starts at one spot.
EPA's household leak checklist gives the habit that catches small leaks early: "Check for pooling water under pipes and rust around joints and edges."[7] For step-by-step repairs once you have found the joint, see how to fix a leaking pipe under a sink.
Stop and call a pro if
- Water has reached an outlet, the disposal's plug or cord, or any wiring under the sink. Stay out of the water and keep your hands off the equipment: "Do not touch electrical equipment if it is wet or if you are standing in water."[8] Call an electrician before anyone works in the cabinet.
- Water is coming from the wall or floor, or the cabinet stays wet while every joint is dry. EPA warns that moisture or mold on walls, ceilings or floors could mean a pipe is leaking behind the scenes and needs a professional.[7]
- A shutoff valve leaks or will not close. If you need to stop a supply leak now, Moen's instruction is: "Rotate the shut offs clockwise until they are tightly closed."[3] If they will not, use the main valve and call a plumber.
- The drain pipe in the wall is cracked or corroded, or it moves when you touch the trap.
- The disposal leaks from its body, or it is hard-wired and needs to come out.
- The cabinet has mold or soft wood. "It is important to dry water-damaged areas and items within 24-48 hours to prevent mold growth."[9] If mold growth covers more than 10 square feet, EPA says to consult its guide Mold Remediation in Schools and Commercial Buildings, which it says applies to other building types too.[9]
Getting help in Virginia
If the leak turns out to be the faucet itself, it may be time for a new one; see how to replace a kitchen faucet, or leaky faucet repair. Loclis lists DPOR-licensed plumbing businesses with their licence number and class: find plumbers in Blacksburg or read more plumbing answers.
When you want a plumber to look at it, describe the leak once and licensed local plumbers quote it.
Common questions
- Why does my sink only leak when I run the dishwasher?
- The dishwasher drains through a hose into the garbage disposal or the sink drain. Check the hose and its clamp where it connects; Moen says the connector and clamp need to be tight and should be replaced if damaged or deteriorated.
- Can I use thread tape to stop a leaking drain trap?
- Usually not. Oatey's answer to that question is "Usually, no," because slip-joint connections seal with washers, not thread tape. If a trap nut leaks, reseat or replace the washer with its tapered side facing the fitting, then snug the nut by hand and a quarter-turn with pliers.
- Is it normal for pipes under the sink to be wet in summer?
- Cold water pipes can sweat in humid weather, which looks like a leak. Dry the pipe and watch it: condensation forms evenly along the cold pipe, while a leak starts at one joint and drips from there.
- The cabinet floor is wet but every joint is dry. What now?
- Check the countertop and faucet base for water getting in from above, then look at the wall behind the cabinet. EPA says moisture or mold on walls, ceilings or floors can mean a pipe is leaking behind the scenes and needs a professional.
- How fast do I need to dry the cabinet out?
- Quickly. EPA advises drying water-damaged areas and items within 24 to 48 hours to prevent mold growth. Leave the doors open with a fan blowing in, and replace the cabinet floor if it has swollen or gone soft.
Sources
- [1] Kitchen Faucet: Leaking Under The Sink Base, Moen. Checked October 26, 2026.
- [2] Leak Underneath: Existing Garbage Disposal, Moen. Checked October 26, 2026.
- [3] How To Turn Off The Water Supply To The Faucet, Moen. Checked October 26, 2026.
- [4] When do I need to use thread seal tape, pipe dome or plumber's putty?, Moen. Checked October 26, 2026.
- [5] How to Install a P-Trap, Oatey. Checked October 26, 2026.
- [6] Oatey 101: Stops and Supply Lines, Oatey. Checked October 26, 2026.
- [7] Detect and Chase Down Leaks Checklist, U.S. Environmental Protection Agency, WaterSense. Checked October 26, 2026.
- [8] Floods, Ready.gov, Federal Emergency Management Agency. Checked October 27, 2026.
- [9] A Brief Guide to Mold, Moisture and Your Home, U.S. Environmental Protection Agency. Checked October 26, 2026.
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