Water Leaking Under Sink (Troubleshooting Guide)

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Quick answer
Confirm the symptom
Tools and prep
Step-by-step troubleshooting
Common causes table
Parts matching
When to call a pro
FAQ
Related guides

Quick answer

First, turn off the water supply valves under the sink. Place a bucket to collect water. Check the water supply lines and drain pipes for leaks. Tighten connections or replace damaged parts as needed.

Confirm the symptom

Water pooling under the sink
Damp or wet cabinets
Musty odor under the sink
Water dripping sound when using the faucet or dishwasher
Visible water stains on the cabinet or floor

Tools and prep

Bucket
Towels
Screwdriver (flathead and Phillips)
Adjustable wrench
Plumber's putty or silicone caulk
Replacement parts (if needed)
Turn off water supply valves under the sink
Put on safety gloves and glasses

Step-by-step troubleshooting

Locate the Leak
Do: Inspect the area under the sink for visible leaks.
Observe: Note the location and source of the leak.
Means: Determine if the leak is from the water supply lines or the drain pipes.
Next: Proceed to the appropriate repair step.
Check Water Supply Lines
Do: Inspect the water supply lines for cracks or loose connections.
Observe: Look for water dripping or spraying from the lines.
Means: Tighten loose connections with an adjustable wrench.
Next: If lines are damaged, replace them.
Inspect Drain Pipes
Do: Check the drain pipes for leaks.
Observe: Look for water dripping or pooling around the pipes.
Means: Tighten loose connections or replace damaged pipes.
Next: If the leak persists, check the drain trap.
Examine the Drain Trap
Do: Place a bucket under the drain trap.
Observe: Check for leaks around the trap.
Means: Tighten the slip nuts on either side of the trap.
Next: If the trap is damaged, replace it.
Check the Faucet
Do: Inspect the faucet for leaks.
Observe: Look for water dripping from the faucet base.
Means: Tighten the mounting nut under the sink.
Next: If the faucet is old or damaged, consider replacing it.
Test the Repair
Do: Turn the water supply valves back on.
Observe: Check for leaks under the sink.
Means: Run water through the faucet and dishwasher (if connected).
Next: If the leak is fixed, clean up the area. If not, reassess the issue.

Common causes

Cause	Likelihood	Difficulty	Part often needed
Loose Water Supply Connections Vibration and wear can loosen connections over time.	Common	Easy	Adjustable wrench
Damaged Water Supply Lines Aging or physical damage can cause lines to crack or burst.	Sometimes	Easy–Medium	Replacement water supply lines
Loose Drain Pipe Connections Movement and wear can cause drain pipes to loosen.	Common	Easy	Adjustable wrench
Damaged Drain Pipes Corrosion or physical damage can cause drain pipes to leak.	Sometimes	Medium	Replacement drain pipes
Faulty Drain Trap A worn or damaged trap can cause leaks.	Sometimes	Medium	Replacement drain trap
Leaky Faucet Base A loose or damaged faucet can cause water to leak from the base.	Sometimes	Easy–Medium	Plumber's putty or silicone caulk

Parts matching

Ensure you have the right parts before starting the repair.

Water supply lines (match the size and type of your existing lines)
Drain pipes (match the size and type of your existing pipes)
Drain trap (match the size and type of your existing trap)
Plumber's putty or silicone caulk (for sealing)
Adjustable wrench (for tightening connections)
Screwdriver set (for disassembling and reassembling parts)

Take a photo of the parts before disassembly to aid in reassembly.

When to call a professional

If the leak is severe and water cannot be contained
If you cannot identify the source of the leak
If the sink or plumbing is old and needs replacement
If you are not comfortable performing the repair
If the leak persists after attempted repairs
If the leak is from a hidden or inaccessible area

FAQ

How do I turn off the water supply to the sink?

Locate the water supply valves under the sink and turn them clockwise to shut off the water.

What if the leak is from the dishwasher connection?

Check the dishwasher hose for leaks or loose connections. Tighten or replace as needed.

Can I use duct tape to fix a leak?

Duct tape is not a reliable long-term fix for plumbing leaks. Use plumber's tape or replace damaged parts.

How do I clean up after the repair?

Wipe down the area with a damp cloth and dry it thoroughly. Dispose of any damaged parts responsibly.