Introduction: Why a Small Leak Demands Immediate Attention

A leaking faucet supply line is more than an annoyance—it can waste hundreds of gallons of water over months and silently damage cabinets, flooring, and drywall. Even a slow drip often indicates failing fittings, a worn hose, or corrosion that can suddenly turn into a burst. Fortunately, with basic tools and a methodical approach, you can stop the leak quickly and avoid costly repairs. This guide covers every step from diagnosis to final testing, including how to choose the right replacement supply line and apply proper sealing techniques.

Understanding Faucet Supply Lines

Supply lines connect your home’s plumbing to the faucet. They are typically made from braided stainless steel, woven nylon, or solid copper tubing. Braided stainless steel is the most common and most durable, but all lines have a finite lifespan. Common failure points include:

  • Cracked or corroded nuts at the shut-off valve or faucet tailpiece.
  • Pinhole leaks or bulges in the hose itself, especially on older rubber lines.
  • Loose connections from temperature changes or vibration.
  • Mineral buildup on threads preventing a proper seal.

Identifying the exact leak source—whether from the supply line body, the compression nut, or the faucet connection—determines whether you can simply tighten or must replace the line.

Tools and Materials You Will Need

Before starting, gather the following. Having everything ready avoids trips to the hardware store mid-repair.

  • Adjustable wrench or two (one to hold, one to turn) – 8- to 10-inch size is ideal.
  • Basin wrench (optional) for tight spaces under the sink.
  • Replacement supply line (if needed) – measure the existing line’s length and verify connection types (1/2-inch or 3/8-inch compression, male/female).
  • Teflon plumber’s tape (thread seal tape) – standard white for water lines, or a thicker pink tape for high-temperature use.
  • Plumber’s putty or pipe joint compound (optional) for certain metal-to-metal connections.
  • Bucket or pan to catch residual water.
  • Rags and a towel for cleanup.
  • Flashlight – under-sink areas are notoriously dark.

Step-by-Step Repair Process

1. Shut Off the Water Supply

Locate the stop valves directly under the sink—one for each faucet supply line. Turn each valve clockwise until fully closed. If the valves are stuck or do not exist, shut off the main water supply to the house. Then open the faucet (both hot and cold handles) to relieve pressure and drain remaining water. Place your bucket under the supply line connections.

Pro tip: If you cannot turn the valve by hand, use a wrench gently. If the valve appears corroded or leaks when turned, plan to replace it later—but for now, closing it should be enough to stop flow.

2. Diagnose the Leak Source

Dry all visible parts with a rag, then inspect thoroughly with a flashlight:

  • Nut at shut-off valve: If water is dripping from the base of the valve or the nut, the compression ferrule or O-ring may be failing. Tighten the nut slightly (1/8 turn); if leak stops, done. If not, the supply line end needs replacement.
  • Supply line body: Look for bulges, cracks, or wet spots along the braided hose. If the braid is rusted or the inner tube is exposed, replace immediately.
  • Faucet connection: Leaks at the top nut where the supply line meets the faucet tailpiece often indicate a loose connection or a missing washer. Disconnect and inspect the rubber gasket.

If the leak is at a threaded fitting and the line appears otherwise sound, you may achieve a quick fix by applying fresh plumber’s tape and retightening. But if the line shows any age, damage, or if the leak recurs, full replacement is the safer route.

3. Remove the Old Supply Line

Place a rag under the connections to catch drips. Using your adjustable wrench, loosen the hexagonal nut that attaches the supply line to the shut-off valve. Turn counterclockwise. Next, loosen the nut at the faucet tailpiece. If the line is long, coil it carefully to avoid splashing.

Important: Some older faucets use a plastic tailpiece that can crack under stress. Support the faucet base with one hand while loosening the nut. If the nut is stubborn, spray penetrating oil and wait five minutes.

4. Clean the Connection Threads

Once the line is removed, clean the threads on both the shut-off valve and the faucet tailpiece using a rag or a small wire brush. Remove any old plumber’s tape, mineral deposits, or rust. Debris left on threads will prevent a proper seal, causing the new line to leak.

5. Apply Plumber’s Tape (Thread Seal Tape)

Wrap Teflon tape clockwise (as you face the end of the pipe) around the male threads of the shut-off valve and the faucet tailpiece. Use 5–6 wraps for a solid seal. Pull the tape tight to embed it in the threads. Do not tape the first thread (nearest the end) to avoid tape bits entering the water supply. If your fittings are compression-type (common on newer valves), tape is still beneficial but not always required—follow manufacturer instructions.

6. Install the New Supply Line

Select a replacement line of the same type and length. Most faucets use 1/2-inch female compression fittings at both ends, but always confirm. Hand-tighten the new line onto the shut-off valve first, then onto the faucet. Once hand-tight, use your wrench to give each nut an extra 1/4 to 1/2 turn—never overtighten, as this can crack plastic or strip threads. The connection should be firm but not forced.

Braided vs. rubber vs. copper: For long-term reliability, choose braided stainless steel with a burst rating of 200+ psi. Rubber lines are inexpensive but degrade faster; copper is durable but rigid and requires flaring tools. Braided lines are DIY-friendly and come with pre-attached nuts.

7. Turn Water Back On and Test

Slowly open the shut-off valve (counterclockwise) while checking for drips. If the valve is new, open only partway and look for leaks before full opening. If you installed the line correctly and used tape, there should be no leakage. If a tiny drop appears, tighten the nut an additional 1/8 turn. Do not turn the valve on fully until you are confident the fittings are dry.

Troubleshooting Common Post-Repair Leaks

Leak at the Supply Line Nut After Tightening

This usually indicates a cross-threaded connection, a cracked nut (too much torque), or a missing rubber washer inside the compression fitting. Remove the line, inspect the washer, and hand-start the nut carefully. If the nut is cracked, replace the entire line.

Leak Inside the Braided Hose

If water seeps through the braiding, the inner tubing has failed—replace the line. There is no repair. Check the burst rating; some cheap lines fail prematurely.

Leak at the Faucet Tailpiece

The O-ring or rubber cone washer inside the faucet base may be worn. You can buy a universal faucet supply line O-ring kit. Disconnect the line, replace the O-ring, and reassemble. This is a separate repair from the supply line itself.

Preventive Maintenance to Extend Supply Line Life

Once your repair is complete, adopt these habits to avoid future leaks:

  • Check supply lines every six months for bulges, rust, or moisture at the nuts.
  • Replace any line that is more than ten years old, even if it looks fine.
  • Never pull or move a supply line side to side; that stresses the connections.
  • Insulate lines in unheated areas to prevent freeze expansion.
  • Install water alarms under sinks to catch micro-leaks early.

When to Call a Professional

Most supply line repairs are well within a DIYer’s capability. However, call a plumber if:

  • The shut-off valve is stuck, broken, or cannot be fully turned off.
  • You encounter pipes that were soldered directly to the faucet (rare in modern homes).
  • You cannot identify the fitting size or type.
  • The leak returns after a second tight attempt—tightening too many times can damage the valve seat.

For reliability, choose a supply line with brass or stainless steel nuts and a PVC or EPDM rubber hose encased in 304 stainless steel braiding. Popular options include:

  • Fluidmaster 1/2-inch braided stainless steel supply line – known for easy installation and durable construction.
  • Everbilt 3/8-inch x 1/2-inch braided line – common for standard kitchen and bathroom faucets.
  • Plumbshop 20-inch supply line – good for compact under-sink spaces.

Always measure the distance between the shut-off valve and the faucet tailpiece, then buy a line that is slightly longer (2–4 inches) to avoid tension. This sizing guide from Faucet.com helps you confirm the right length.

Final Thoughts

A leaking faucet supply line is one of the most common plumbing repairs in any home, and it is almost always fixable without a plumber—provided you diagnose the problem correctly and use the proper replacement part. By following the steps above, you can stop the leak in under an hour, protect your home from water damage, and extend the life of your faucet. Remember: never ignore a drip, and always test thoroughly before leaving the sink. For more advice on preventing plumbing emergencies, check out This Old House's guide to water damage prevention. And if you need to replace a shut-off valve, Family Handyman’s step-by-step tutorial is an excellent resource.