Quick answer
Turn off the water supply to the sink. Check the valve handle and stem for damage. Replace the washer or O-ring if worn, or install a new valve if damaged.
Confirm the symptom
- Water dripping from under the sink near the valve
- Visible moisture or puddles near the valve
- Dripping sound when the valve is off
- Leak worsens when the valve is turned
Tools and prep
- Adjustable wrench
- Plumber's tape
- Replacement washer or O-ring
- Bucket or towel to catch water
- Shut off water supply to the sink
- Protective gloves and eyewear
Step-by-step troubleshooting
- Turn Off Water SupplyDo: Locate and turn off the shut-off valves under the sink.Observe: Water stops flowing from the faucet.Means: Water supply is safely off.Next: Check valve for visible damage
- Check Valve for DamageDo: Inspect the valve handle, stem, and connections for cracks or wear.Observe: Visible cracks, corrosion, or worn parts.Means: Damaged parts may need replacement.Next: Tighten or replace parts
- Tighten Valve ConnectionsDo: Use an adjustable wrench to gently tighten the valve connections.Observe: Leak stops or reduces.Means: Loose connections were the issue.Next: Test valve operation
- Test Valve OperationDo: Slowly turn the valve on and off to check for leaks.Observe: No water leaks from the valve.Means: Valve is functioning properly.Next: Replace washer or O-ring if needed
- Replace Washer or O-RingDo: Remove the valve handle and stem to access the washer or O-ring. Replace with a new one.Observe: Leak stops after replacement.Means: Worn washer or O-ring was the cause.Next: Reassemble and test
- Reassemble and TestDo: Reassemble the valve components and turn the water supply back on.Observe: No leaks and proper water flow.Means: Repair is successful.Next: Monitor for recurring leaks
Common causes
| Cause | Likelihood | Difficulty | Part often needed |
|---|---|---|---|
| Worn Washer or O-Ring Sealing components degrade over time, causing leaks. | Common | Easy | Washer or O-Ring |
| Loose Valve Connections Vibrations or infrequent use can loosen fittings. | Common | Easy | Plumber's Tape |
| Damaged Valve Stem Corrosion or physical damage can prevent proper sealing. | Sometimes | Medium | Valve Stem |
| Faulty Valve Seat Wear or mineral buildup can prevent a tight seal. | Sometimes | Medium | Valve Seat Repair Kit |
| Broken Valve Handle A cracked or broken handle can cause water to escape. | Rare | Easy | Valve Handle |
| Corroded Valve Body Mineral deposits or rust can compromise the valve structure. | Rare | Hard | New Valve |
Parts matching
Common parts needed for a leaking valve under the sink include:
- Washer or O-Ring
- Plumber's Tape
- Valve Stem
- Valve Seat Repair Kit
- Valve Handle
- New Valve (if damaged)
Take the old part to the hardware store to ensure a proper match.
When to call a professional
- Leak persists after replacing washers and O-rings
- Valve is corroded or damaged beyond simple repair
- You're unsure about shutting off the water supply
- You don't have the tools or confidence to complete the repair
- Leak is causing significant water damage or mold growth
FAQ
How do I know if the valve is the source of the leak?
Check for water dripping from the valve itself or pooling around its base when the water is off. If the leak stops when the valve is closed, it's likely the issue.
Can I fix a leaking valve without replacing it?
Yes, if the issue is a worn washer or loose connection. Replacing these parts can often stop the leak without replacing the entire valve.
What if the water supply shut-off valve is leaking?
If the shut-off valve itself is leaking, you may need to replace it. Turn off the main water supply to the home before attempting this repair.
How often should I check for leaks under the sink?
Inspect under the sink monthly for signs of leaks, especially if you notice reduced water pressure or higher water bills.
Can a leaking valve cause higher water bills?
Yes, even a small leak can waste significant water over time, leading to higher utility bills. Fixing it promptly can save money.