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How to Fix a Sink Water Leak (Step-by-Step)

How to Fix a Sink Water Leak (Step-by-Step)

A leaking sink can waste water and cause cabinet damage fast. The good news: many sink leaks come from a few common spots—supply lines, shutoff valves, the drain trap, or the faucet itself. Here’s a safe, homeowner-friendly way to diagnose and fix the most common sink water leaks.

Before you start (safety + tools)

  • Turn off water at the shutoff valves under the sink (hot and cold).

  • Place a towel and a bucket under the plumbing.

  • Tools: adjustable wrench, channel-lock pliers, flashlight, rag, and (optional) plumber’s tape.

Step 1: Find where the leak is coming from

Dry everything under the sink, then turn the water back on briefly and watch closely with a flashlight. Leaks usually show up in one of these areas:

  • Supply lines (flex hoses) connecting the shutoff valves to the faucet

  • Shutoff valves (packing nut or valve body)

  • Drain connections (P-trap slip nuts, tailpiece, disposal connection)

  • Faucet base or handles (leak above the cabinet floor)

Step 2: Fix common under-sink leaks

A) Leaking supply line connection

With water OFF, snug the nut at the valve and at the faucet connection (a small turn—don’t over-tighten). If it still leaks, replace the supply line; they’re inexpensive and often the fastest fix.

B) Leaking shutoff valve

If water seeps from the valve handle area, gently tighten the packing nut (the small nut behind the handle). If the valve body leaks or won’t shut off fully, it’s safer to have a plumber replace the valve.

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C) Leaking P-trap or drain slip nuts

Hand-tighten slip nuts first. If it still drips, loosen the nut, check that the washer is seated correctly, then re-tighten. Cracked plastic traps or worn washers should be replaced.

Step 3: If the leak is from the faucet

Leaks at the faucet base or handles often mean worn cartridges, O-rings, or seals. Many faucets have repair kits, but the steps vary by brand. If you can identify the faucet model, you can usually replace the cartridge and stop the leak.

When to call a plumber

  • You can’t fully shut off the water at the valves

  • There’s corrosion, damaged pipes, or a leak inside the wall

  • The leak returns after tightening/replacing basic parts

Find a plumber on Ready Jan

If you’d rather have a pro handle it, Ready Jan helps you find and compare local plumbers by service area and specialty. Send a job request with your issue, location, and photos (if you have them) to get faster, more accurate responses. ReadyJan.com

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