Why Is Water Leaking Under My Sink?

Leaking water under the sink can be caused by a number of problems. At Terry’s Plumbing, we encounter leaks under the sink all the time, but find that the reasons behind these problems can be varied. In this post, we’ll cover some of the most common causes of water leakage under the sink and suggest solutions that can help.

Diagnosing the Problem

Looking under your sink, you’ll see multiple potential sources for a leak. Water supply lines usually run at the back and may cross over to the dishwasher, if you have one. Coming down from the sink, you’ll see the drain pipe connected to a squiggly pipe known as the P trap. Leaking water can come from any one of these lines, and if you have a garbage disposal, could be coming from the disposal as well.

Observe. To diagnose your problem, start by observing the puddles when they form. Look for dripping water, signs of corrosion, rust and other problems that could be the cause of a leak. If you see no obvious source of the leak, run the water in your sink and then look under the sink and watch for moisture to gather. Allow your garbage disposal to fill up, and test all parts of the sink, including the spray hose and both hot and cold water supplies. If after running your sink for several minutes you see no leak at all, run your dishwasher and continue to watch for signs of a leak.
Run a tissue over all surfaces. If the source of the water continues to be a mystery, touch all of the supply and drain lines with a tissue to detect moisture on the lines, then wipe down the entire interior of the cabinet to find out where water is (and where it isn’t). While you’re at it, touch the supply lines where they connect to the faucet. This may be in a hard to reach place behind the sink.

Tightening Connections

Often the source of the leak is a loose connection between a line and a valve. To tighten the connection between a line and a valve, use one wrench to hold the valve and use a second wrench to tighten the compression fitting. If the connection continues to be loose, this could be a sign of dirt or sediment in the pipe around the fitting. To clear out the dirt, turn off the water supply and disconnect the supply line. Clean the fitting with a cloth, line the fitting with Teflon tape, then reattach.

If you determine that the source of the leak is a connection around the drain line P trap, use a wrench to tighten metal fittings or use your hands to tighten plastic fittings. If this doesn’t work, detach the pipes and clean them out. Line the joint with Teflon tape, then reconnect. Water will be trapped in the P trap, so you’ll need a bucket on hand to catch what comes out of the pipe.

Know When to Contact Terry’s Plumbing

If you’ve tried everything suggested above and you haven’t been able to find the source of the leak or fix the leak, this is a good time to get professional help. At Terry’s Plumbing, we help people just like you to maintain their home’s plumbing and avoid costly disasters. If you live in or around Pittsburgh and need help with your plumbing, or if you have a leak you just can’t seem to fix, contact us today. We can help you determine the source of your problem and can also make repairs.