Water Under the Sink: Stop the Leak, Find the Source, and Prevent Cabinet Damage
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Water Under the Sink: Stop the Leak, Find the Source, and Prevent Cabinet Damage
Disclosure: This article is for general information only. If you can’t stop the leak quickly or water is near electrical outlets, shut off power and contact a licensed plumber.
Quick Answer
First, figure out if it’s a supply leak (pressurized) or a drain leak (only leaks when water runs).
Supply leaks can flood fast. Shut off the valve immediately.
Drain leaks usually give you time, but they still cause swelling, odor, and mold if you wait.
Why the First 10 Minutes Matter (Real Numbers)
A kitchen faucet is allowed up to 2.2 gallons per minute. If a pressurized line is leaking, that can become a lot of water in a short time.
And EPA notes that if wet materials are dried within 24–48 hours, in most cases mold will not grow. That’s your cleanup window.
Stop the Damage First (0–3 Minutes)
Step 1) Kill the water at the right valve
Open the cabinet. Look for two small shutoff valves (hot and cold).
Turn the leaking side clockwise until it stops.
If you can’t find the exact leak or the valves won’t close, shut off the main water.
Step 2) Catch and dry
Put a bowl under the drip.
Pull everything out of the cabinet.
Towel dry. Then airflow. Fan + cabinet doors open.
Aim to dry everything as soon as possible within that 24–48 hour window.
Find the Leak Fast: Supply vs Drain (The 30-Second Test)
If it leaks even when no water is running
That’s usually supply-side (pressurized):
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Angle stop valve (the shutoff itself)
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Supply line (braided hose)
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Faucet connections
If it leaks only when you run the faucet
That’s usually drain-side:
The 9 Most Common Leak Points (Check in This Order)
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Shutoff valve stem (drip at the handle)
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Supply line nut (wet at the top of braided hose)
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Supply line itself (bulge, corrosion, pinhole spray)
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Faucet base (water pooling above, then dripping down)
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P-trap slip joints (drips only when water runs)
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Trap bend (hairline cracks or misalignment)
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Garbage disposal discharge (wet around clamp/gasket)
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Dishwasher drain hose (drips during drain cycle)
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Cabinet bottom seam (water traveling from somewhere else)
Tip: Use dry paper towel “taps” on each connection. The first wet spot usually reveals the leak.
What You Can Do Safely (And What You Shouldn’t)
Safe DIY checks
Tighten a loose slip nut by hand (drain side).
Re-seat a tilted P-trap if it’s obviously misaligned.
Dry everything and retest with a small flow of water.
Don’t do this
Don’t crank fittings hard with tools unless you know the connection type.
Over-tightening can crack plastic parts or deform seals.
When to Call a Plumber Immediately
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Leak continues after you shut off the cabinet valves
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You see a spray or fast drip from a pressurized line
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Cabinet walls are swelling, flooring is buckling, or you smell musty odor
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You suspect the leak is inside the wall
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Any electrical risk near outlets or disposal wiring
Costs (So You Can Spot a Wild Quote)
HomeAdvisor’s national guidance shows:
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Plumber service call fees often $100–$250, usually including the first hour.
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General plumbing labor is commonly $45–$200/hour, with many jobs averaging $175–$450 total.
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Leaking pipe repair is often $150–$350, and diagnosing leak locations can add about $100 (before wall repair).
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If walls must be opened, drywall repair can add $250–$750.
Angi notes leak repairs can range widely depending on location and damage, with an average around $500.
Scam Prevention (5 Rules That Save Money)
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If they say “major repipe,” ask: Where is the leak and how did you confirm it?
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Don’t approve wall demolition without a clear written scope and leak confirmation.
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Get itemized pricing (service call, labor, parts, drywall/cleanup).
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Avoid paying the full amount upfront. FTC warns against full upfront payment.
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If the plan jumps from a simple leak to “thousands,” get a second estimate.
Next Steps
【Internal Link①】Home Emergency Checklist: Stop Damage in the First 30 Minutes
【Internal Link②】Home Repair Cost Guide: Repair vs Replace (What Really Changes the Price)
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