The short answer
Clear the Cabinet and Dry Everything
Pull out all cleaning supplies, sponges, and anything else stored under the sink. Lay down a dry towel or paper towels on the cabinet floor. This gives you a clean, dry base to spot new moisture. It also keeps items from soaking up water and hiding the leak.
Run Water and Watch for Drips
Turn on the cold water full force. Let it run for a minute or two while you watch the supply line and the valve. Then do the same with the hot water. Move the faucet sprayer around and check the hose connection. Run water down the drain and look for leaks at the P-trap and the drain flange.
Keep a flashlight handy to see into tight spots. Shine it on each joint and fitting. If you see a drip or a growing wet spot, that is your leak. If nothing shows, dry everything again and repeat. Sometimes a leak only appears when the water pressure changes or when the sprayer is used.
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- Check the base of the faucet where it meets the sink.
- Inspect the sprayer hose connection under the handle.
- Look at the slip nuts on the P-trap.
- Feel the shutoff valves for moisture on the handles.
- Examine the supply line where it attaches to the valve.
- Run water slowly, then fast, to see if the leak changes.
Use a Dry Paper Towel Test
Fold a paper towel into a small square and press it against each pipe joint and fitting. Hold it there for about ten seconds. Remove it and check for any dampness. This method helps you catch slow seeps that may not form visible drips. It also keeps your fingers from confusing water with condensation.
Work your way from the top of the plumbing down to the floor. Test the faucet base, the supply lines, the shutoff valves, the drain pipe, and the P-trap. If a towel comes away wet, you have found the spot. Mark it with a piece of tape or take a photo so you remember exactly where it is.
- Press the towel firmly against each joint for a full ten seconds.
- Use a fresh towel for each spot to avoid spreading moisture.
- Check the drain gasket where it meets the sink basin.
- Look at the back of the cabinet where pipes pass through.
- Feel the floor under the P-trap for hidden drips.
Trace Water Back to Its Source
If you see water pooling on the cabinet floor but cannot find a drip on any pipe, the leak may be coming from above. Run water in the sink and watch the underside of the basin. A crack or failed seal can let water run down the outside of the drain pipe. That water may travel along the pipe before dripping off.
Another possibility is a leak from the faucet base that runs down the countertop and into the cabinet. Wipe the countertop dry and run the faucet. Check the area where the faucet meets the sink. If the leak only happens when the sprayer is used, the hose or its connection is the likely culprit.
- Run water and watch the underside of the sink basin.
- Check the countertop around the faucet for moisture.
- Use a mirror to see behind the pipes if space is tight.
- Look for water stains on the cabinet floor or walls.
- Feel the cabinet floor for dampness after running water.
Know When to Call the Pros
If you find a leak but cannot stop it by tightening a fitting or replacing a washer, turn off the shutoff valves under the sink. Use the sink as little as possible until the issue is fixed. A persistent leak can soak the cabinet, the floor, and even the wall behind the sink. That moisture can lead to wood rot and mold growth.
- Turn off the shutoff valves if the leak is severe.
- Place a bucket under the leak to catch drips.
- Wipe up standing water to prevent further damage.
- Check the area daily for musty odors or discoloration.
- Keep the cabinet door open to help things dry out.
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Call Now (480) 898-4279Frequently asked questions
Why is there water under my sink but no visible leak?
Water can travel along pipes before dripping, so the source may be higher up. Check the faucet base, the sprayer hose, and the drain flange. Condensation on cold pipes can also cause dampness, especially in humid weather. Dry everything and run each water source separately to isolate the cause.
Can I fix a small leak under the sink myself?
Yes, if it is a loose slip nut or a worn washer, you can often tighten it or replace the part. Turn off the shutoff valves first. Use a wrench to snug fittings but avoid overtightening, which can crack plastic. If the leak persists or the pipes are corroded, call a plumber.
What should I do if the leak has already caused damage?
Turn off the water and dry the area with towels. Remove any wet cardboard boxes or paper items. If the cabinet floor is swollen or the wall is stained, the moisture may have spread further. Local water damage pros can assess the extent and dry the area properly to prevent mold.