Water Under Sink but No Leak? 9 Potential Causes and How to Find Them
Find out why water sometimes pools under the sink and learn how to identify the cause
Highlights
Loose nuts or worn parts can cause sink leaks.
The solution could be as simple as tightening parts with pliers.
You may need to replace valves, hoses, caulk, and more.
Uh-oh! You've noticed moisture under the sink. Worse yet, you can't figure out where the leak is coming from, and it's driving you nuts. Know that water under the sink but no leak is a common problem since sinks will inevitably require maintenance from time to time. It’s just a matter of figuring out if you can fix it yourself or if you need to call a plumber in your area. Here are some possibilities for the cause of your mystery leak.
1. Loose Nuts
Because the plumbing under your sink has both hot and cold water running through it, it’s normal for pipes to expand and contract. Over time, this could mean that the connections that keep the piping together can become loose. Check the water supply lines and drain lines for this type of leakage.
This issue is easy to fix once you locate the source of the leak. Tighten the nuts with your hands, and then use pliers if necessary.
2. Worn-Out Washers
If you’ve tried tightening any loose nuts and you’re still seeing moisture, check the washers. A washer in good shape is smooth and round, while worn-out washers can have cracks and worn edges. You can easily replace them to fix the problem.
3. Shutoff Valves
Plumbing maintenance tips often include checking the shutoff valves and O-ring to prevent leaks. This is because it’s common for shutoff valves to leak due to gaskets or O-rings that wear out over time. These parts typically last around 10 to 15 years, so it may simply be time to replace the unit
4. Leaking P Trap
The P trap under your sink is the curved portion of the piping that catches extra debris. If this is leaking, the first thing to try is tightening the coupling nuts and checking the washers. You should clean out the P trap if that doesn't fix the leak.
5. Leaking Sink Drain Trap
Components in the sink drain trap can wear out, which may require you to either reseal it with plumber’s putty or replace the rubber gasket. In many cases, it’s easier to do a full replacement rather than hunting down specific replacement parts.
6. Leaking Spray Nozzle
If your leak is coming from the cabinet ceiling, it may be a leaking spray nozzle. Tighten the stem connection on the hose, but if that doesn’t work, you’ll likely need to replace the hose and nozzle. If they’re a standard design, you may be able to find spare parts at the store. Otherwise, it may be easier to buy a replacement.
7. Leaking Garbage Disposal
If the leak is at the top of the garbage disposal, the culprit may be the sink flange, which is the part that connects the garbage disposal to the sink. The flange may need to be tightened or replaced, or you may need to install fresh plumber’s putty.
If the disposal is leaking at the bottom, the best-case scenario is a worn-out flywheel gasket. However, if the issue is with the internal seal or a crack in the housing, you will likely need a new disposal. Depending on your skill set, consider calling a pro to help with the garbage disposal installation.
8. Leaking Dishwasher Parts
The dishwasher's drain hose connects it to the garbage disposal. Try tightening the metal clamp if the leak only happens during a dishwasher cycle. You may also need to replace the hose.
9. Leaking Due to Old Caulk
The caulk around your sink can crack and become brittle over time. When this happens, water can leak between the sink and the counter. You can re-caulk the sink to fix this problem. Signs that you should replace the caulk include cracks, empty gaps, discoloration, and tiles coming loose.
How to Find a Leak Under the Sink
You've checked the common culprits of what could be causing the moisture under your sink, but you still need help. You can do a few things to solve the mystery, and it's worth putting in the extra effort.
And in the future, start paying attention to small water leaks to prevent bigger issues down the road.
Clean the Cabinet
The first thing you should do is to clean the cabinet. Pull out anything you’ve been storing under the sink while making sure that any hazardous or poisonous items are out of reach from children and pets. Next, do a quick scan with a flashlight—you might be able to spot the source of the leak.
Use a towel and wipe down all the pipes and cabinet walls. If you couldn’t visually find the leak, you might find it while cleaning.
Use Paper Towels to Identify Dripping
If you still can’t figure out the source of the leak, place a couple of layers of paper towels on the cabinet floor. Check it every hour or so until you notice wetness on the paper. You might have to leave it overnight.
Eventually, you’ll notice moisture on the paper towels. Look above the wet spots for the leak source. Run your hands along the piping, ceiling, hoses, valves, and nuts until you feel moisture.
Wrap Toilet Paper Around the Pipes
If you suspect the leak is coming from a pipe and can't pinpoint its location, wrap it with toilet paper. This will make it easier to spot the leak.
Put the Pipes Under Duress
If you’re stumped after trying the paper towel and toilet paper methods, you can move forward with the basin test. It’s simple enough to do: Plug both of your basins and fill them with water.
Next, unplug the stoppers at the same time and let the water rush through your pipes. Turn your garbage disposal on as the sink drains, and see if you can spot any leaks. If everything looks fine, turn on your dishwasher for several minutes, stop it, and drain it to see if the appliance is the issue.
Forcing your pipes to deal with a large amount of water can help you figure out the source of the leak. Prepare beforehand by laying down towels on the cabinet floor and the kitchen floor by your dishwasher.
Test the Faucet, Too
Additionally, check out your faucet to see if it's the culprit. In some cases, your faucet may not leak, except for the rare instances when you use the sprayer. To determine if your faucet is the source of the issue, put it through its paces and test all its modes and features.
Also, common issues like a corroded valve seat or an old gasket will require a quick and easy replacement. If your faucet is old, you may need to replace it too, because faucet parts will deteriorate over time.
When to Call a Plumber to Fix a Leak
If you've tried everything you can to find the source of the leak to no avail, it’s a good time to hire a plumber near you. Bringing in a pro may be your only option if your problem extends beyond a simple fix, like replacing a washer or emptying a P trap. For example, hiring a plumber for bigger projects, like replacing corroded piping or installing replacement appliances, is a good idea. Note that bathroom leak repair costs around $150 to $350, while the average cost to fix a leaking pipe is $500.
It's also advisable to bring in help as soon as possible because even a small leak can cause significant problems. Water-damaged cabinets and vanities may require repair or even a costly replacement. Plus, fixing the problem is necessary for you to avoid being hit with an unexpectedly high water bill. This also goes for similar issues like bathtub overflow drain leaks, which can cause water damage to your flooring.
Besides having your leak fixed, you can also ask your plumber to conduct plumbing maintenance while they’re there. It’s a good way to nip potential issues in the bud before they get any worse.