How Do I Stop a Pipe From Leaking Under the Sink?
Last updated October 28, 2026
The short answer
Shut off the Water
The first step is to stop the flow of water. Look under the sink for two shutoff valves, one for hot and one for cold. Turn them clockwise to close. If you cannot find them or they do not work, shut off the main water valve for your home, often located near the water meter or where the main pipe enters the house.
Once the water is off, open the faucet to release any remaining pressure and drain the pipes. Place a bucket or towel under the leak to catch drips. This gives you a dry, safe area to work. If you live in Redmond, keep the location of your main shutoff valve written down for quick access.
Inspect the Leak
Dry the pipes and fittings with a rag. Look for the source of the leak. Common places are the slip joint nuts where pipes connect, the supply lines to the faucet, or the drain trap. Check for cracks, corrosion, or loose fittings. A small drip often comes from a loose nut, while a steady spray may mean a damaged pipe.
Feel around the connections with your fingers. If you find moisture, note the exact spot. For threaded connections, try tightening them gently with a wrench. Do not overtighten, as that can crack the fitting. If the leak continues, the problem may be a worn washer or a cracked pipe that needs replacement.
- Turn off both hot and cold shutoff valves
- Open the faucet to drain remaining water
- Dry all pipes and fittings thoroughly
- Check slip joint nuts and supply lines
- Feel for moisture at every connection
- Tighten loose nuts with a wrench
Tighten Connections
Many leaks under the sink are simply loose connections. Use an adjustable wrench to tighten the slip joint nuts on the drain pipe and the nuts on the supply lines. Turn clockwise to tighten. Work slowly and check for leaks after each turn. If the leak stops, you are done for now, but monitor the area over the next day.
For compression fittings, you may need to replace the rubber washer inside. Turn off the water, unscrew the nut, and inspect the washer. If it is flattened or cracked, take it to a hardware store to find a match. Replace it and reassemble. This is a simple fix that often solves the problem.
Replace Damaged Parts
If tightening does not stop the leak, the pipe itself may be damaged. Corroded metal pipes or cracked plastic supply lines need replacement. You can buy replacement supply lines at a hardware store. Measure the length you need and match the fitting type. Turn off the water, disconnect the old line, and install the new one with a wrench.
For the drain trap, a cracked PVC pipe can be replaced by cutting out the damaged section and installing a new trap. This requires a hacksaw and a new trap kit. If the leak is behind the wall or under the floor, you may need a plumber. Do not attempt major repairs if you are unsure, as a bigger leak can cause water damage.
When to Call a Pro
Some leaks are beyond a quick fix. If the leak is in a wall, under the floor, or involves corroded pipes that need soldering, call a plumber. A plumber has the tools and experience to handle complex repairs safely. For water damage that has already occurred, such as soaked cabinets or a wet subfloor, you may need water damage pros for cleanup and drying.
Water damage pros can also help with leak detection. They use specialized equipment to find hidden leaks and assess moisture levels. If you notice warped wood, musty smells, or stains on the ceiling below the sink, call the pros. They can dry the area and prevent mold growth. Ignoring a small leak can lead to bigger problems.
- Leak inside a wall or under the floor
- Corroded pipes that need soldering
- Water damage to cabinets or subfloor
- Musty odor or visible mold
- Persistent leak after tightening and replacing
Talk to someone now
Call (425) 407-5186 any time, day or night, and describe what happened.
Call Now (425) 407-5186Frequently asked questions
How do I find the shutoff valve under the sink?
Look for two small valves, usually chrome or plastic, attached to the hot and cold supply lines. They are often located near the back of the cabinet. Turn them clockwise to close. If they are not there, check the main water shutoff for your home.
Can I use tape to stop a pipe leak temporarily?
Plumber's tape or epoxy putty can stop a small drip for a short time, but it is not a permanent fix. The tape may fail under pressure. Turn off the water and replace the damaged section as soon as possible. Temporary fixes can hide a bigger problem.
What if the leak is from the sprayer hose?
If the sprayer hose is leaking, check the connection at the sprayer head and the base of the faucet. Tighten any loose fittings. If the hose itself is cracked, replace it with a new one. Turn off the water before making any changes.