A leaking pipe under the sink can quickly cause water damage, unpleasant odors, cabinet damage, and even mold if it is left untreated. The good news is that many small leaks can be fixed with basic tools and replacement parts.

The first step is to identify exactly where the water is coming from. A leak may be caused by a loose connection, worn washer, damaged seal, cracked pipe, or blocked drain.

⚠️ Safety first: If water is leaking near electrical outlets, appliances, or wiring, shut off the appropriate water supply and avoid touching wet electrical components. For major leaks or damaged plumbing inside the wall, contact a qualified professional.

🔍 Common Causes of a Leaking Pipe Under the Sink

A pipe under your sink may leak because of:

• Loose pipe connections
• Worn or damaged washers
• Failed rubber seals
• Cracked drain pipes
• Damaged P-trap
• Loose slip nuts
• Corroded metal pipes
• Blocked or partially blocked drain
• Excessive pressure on pipe joints
• Incorrectly installed plumbing
• Aging plumbing components

🛠️ 20 Easy Ways to Fix a Leaking Pipe Under the Sink

1. Turn Off the Water Supply

Before working under the sink, turn off the water supply if the leak involves a supply line.

Look for the shutoff valves beneath the sink and turn them clockwise.

If you cannot stop the water or the leak is severe, shut off the home’s main water supply.

2. Place a Bucket Under the Leak

Put a bucket, bowl, or large container underneath the leaking pipe.

This prevents water from spreading inside the cabinet and makes it easier to identify the source.

Place towels around the area to absorb remaining water.

3. Empty the Sink

Avoid using the sink while you’re diagnosing or repairing a drain leak.

Remove standing water and let the plumbing underneath become as dry as possible.

This makes it easier to see where fresh water appears.

4. Dry the Pipes Completely

Use a clean towel to dry:

• P-trap
• Drain pipe
• Slip nuts
• Washers
• Supply connections
• Nearby joints

Once everything is dry, you can run a small amount of water through the sink and watch carefully for the first point where water appears.

5. Identify Exactly Where the Leak Starts

Don’t assume the lowest wet point is the source.

Water can travel along a pipe before dripping down.

Check each connection from top to bottom and look for:

• Drips
• Wet threads
• Cracks
• Corrosion
• Damaged seals
• Loose connections

Finding the actual source prevents you from repairing the wrong part.

6. Tighten a Loose Slip Nut

If the leak is coming from a drain connection, the slip nut may simply be loose.

Hand-tighten it first.

If necessary, use adjustable pliers for a small additional turn, but don’t overtighten. Excessive force can damage plastic fittings or distort the seal.

7. Check the Washer Inside the Connection

Many sink drain connections use a rubber or plastic washer to create a watertight seal.

A worn washer may become:

• Cracked
• Flattened
• Brittle
• Misaligned

If the connection continues leaking after tightening, remove it and inspect the washer.

8. Replace a Damaged Washer

If the washer is damaged, replace it with the correct size and type.

Clean the connection before installing the new washer.

Make sure the washer sits correctly and evenly before tightening the connection.

9. Inspect the P-Trap

The P-trap is the curved section of pipe underneath the sink.

Check it for:

• Cracks
• Corrosion
• Loose connections
• Damaged washers
• Water dripping from joints

A damaged P-trap is often relatively straightforward to replace if the plumbing configuration is accessible.

10. Clean the P-Trap

A partially blocked P-trap can create drainage problems and contribute to leaks around its connections.

If the design allows safe removal, place a bucket underneath and carefully remove the trap.

Clean out accumulated debris and reinstall it correctly.

Make sure all washers are positioned properly.

11. Check the Sink Drain Connection

Sometimes the leak isn’t actually coming from the pipe.

The connection between the sink drain opening and the drain assembly can also leak.

Run a small amount of water into the sink and watch the underside of the drain opening.

If water appears there, the drain seal may need repair or replacement.

12. Inspect the Faucet Supply Lines

If the leak occurs only when the faucet is running, check the flexible supply lines underneath the sink.

Look for:

• Loose connections
• Damaged hoses
• Corrosion
• Cracks
• Water dripping from the connector

A damaged flexible supply line should generally be replaced rather than patched.

13. Check the Shutoff Valve

Inspect the water shutoff valves beneath the sink.

If water is coming from around the valve or its connection, the valve may be worn or damaged.

Don’t force a stuck valve. If it won’t operate normally or continues leaking, professional plumbing help may be needed.

14. Replace a Cracked Plastic Pipe

Plastic drain pipes can develop cracks due to age, impact, overtightening, or stress.

If you find a visible crack, replacing the damaged section is usually more reliable than trying to seal it permanently with tape.

Use a compatible replacement part of the correct size.

15. Inspect Metal Pipes for Corrosion

Older metal plumbing can corrode over time.

Look for:

• Rust
• Green or white deposits
• Thin or weakened pipe sections
• Small pinhole leaks
• Severe discoloration

If the pipe is badly corroded, avoid repeatedly tightening the connection because the pipe may break.

16. Check for Pipe Misalignment

Drain pipes should connect without excessive force or bending.

If a pipe is being pushed sideways to make a connection fit, the joint can eventually leak.

Repositioning or replacing the incorrectly fitted section may be necessary.

17. Check for a Blocked Drain

A blocked drain can cause water to remain in the plumbing longer and may expose weak connections to repeated stress.

If the sink drains slowly, clear the blockage using an appropriate method before assuming the pipe itself is defective.

Avoid harsh chemical drain cleaners that can create safety hazards.

18. Test the Repair Slowly

After making a repair, don’t immediately fill the sink completely.

Instead:

1. Turn the water supply back on if it was shut off.
2. Run a small amount of water.
3. Watch the repaired connection.
4. Check for fresh moisture.
5. Gradually increase the water flow.
6. Check again underneath the sink.

If the area stays completely dry, the repair is likely successful.

19. Dry and Protect the Cabinet

Once the leak has been fixed, dry the cabinet thoroughly.

Water left underneath a sink can damage:

• Wooden cabinets
• Particleboard
• Flooring
• Stored items

Leave the cabinet open for a while to allow remaining moisture to evaporate.

20. Replace Damaged Plumbing Components

If a pipe, trap, washer, connector, or supply hose is badly damaged, replacement is usually better than repeatedly attempting temporary repairs.

Use parts that match the existing plumbing size and connection type.

If you’re unsure which component to purchase, take the old part to a plumbing-supply store for identification.

📊 Quick Diagnosis Table

⚠️ When to Call a Professional Plumber

DIY repair may not be appropriate if:

• The leak is inside the wall.
• A water supply pipe has burst.
• You cannot shut off the water.
• The pipe is severely corroded.
• Multiple fixtures are leaking.
• Several drains are backing up.
• There is significant water damage.
• You see water near electrical wiring or outlets.
• The repair requires major pipe replacement.
• You are unsure which plumbing component is damaged.

A small visible drain leak can often be handled at home, but a pressurized water-line failure can cause significant damage very quickly.

🧤 Important Safety Tips

• Turn off the water before disconnecting plumbing.
• Keep a bucket under the pipe while working.
• Wear waterproof gloves when handling dirty drain water.
• Don’t overtighten plastic fittings.
• Don’t use excessive force on corroded pipes.
• Avoid mixing chemical drain cleaners.
• Keep electrical devices away from leaking water.
• Don’t ignore a small leak—it can cause cabinet and flooring damage.
• If water reaches electrical components, prioritize electrical safety and professional assistance.

🚿 How to Prevent Future Under-Sink Leaks

You can reduce the chance of future leaks by:

1. Check plumbing connections periodically.
2. Don’t store heavy items against pipes.
3. Avoid hanging objects from plumbing.
4. Fix slow drains promptly.
5. Don’t overtighten plastic fittings.
6. Replace deteriorated washers when necessary.
7. Keep the cabinet dry.
8. Check flexible supply hoses for aging or damage.
9. Watch for corrosion on older pipes.
10. Investigate small drips before they become major leaks.

❓ Frequently Asked Questions

How do I stop a pipe under my sink from leaking?

First, identify the source. If it’s a loose drain connection, carefully tighten it. If the washer, seal, or pipe is damaged, replace the defective component.

Can I fix a leaking pipe with plumber’s tape?

It depends on the connection. Thread-sealing tape is designed for certain threaded plumbing connections, but many sink drain joints rely on washers or compression seals instead. Using tape where a washer is supposed to seal may not fix the problem.

Why is my P-trap leaking?

A P-trap may leak because of a loose connection, damaged washer, crack, corrosion, or incorrect installation.

Should I replace a cracked pipe or seal it?

Replacing a cracked plumbing component is generally more reliable than relying on a temporary patch, particularly for a recurring leak.

Why does my sink pipe leak only when I use the sink?

If water appears only while the sink is draining, the problem is likely somewhere in the drain assembly, P-trap, or drain connections.

Can a clogged drain cause a pipe to leak?

A blockage can contribute to drainage problems and place additional stress on plumbing connections. If a slow drain and leak occur together, address both issues.

How do I know if the leak is from the faucet or pipe?

Dry everything first, then run the faucet while watching underneath the sink. Follow the first appearance of fresh water rather than assuming the lowest wet point is the source.

📝 Final Words

A leaking pipe under the sink is often caused by a loose connection, worn washer, damaged seal, cracked pipe, or P-trap problem. Start by shutting off the water when necessary, drying the plumbing, and identifying the exact source of the leak.

For a simple joint leak, tightening the connection or replacing a washer may solve the problem. However, badly corroded pipes, pressurized supply-line leaks, hidden leaks, and major water damage should be handled by a qualified plumber.

Fixing a small leak early can help prevent much more expensive cabinet, flooring, and plumbing damage later.