Replace a Water Supply Line
Shut off the water, disconnect the old supply line with an adjustable wrench, then hand-tighten the new braided stainless steel line to both the shutoff valve and fixture tailpiece before turning the water back on.
- Difficulty
- Beginner
- Time
- 20-30 minutes
- Cost
- $8-$18
- Tools
- Adjustable wrench, Basin wrench (for hard-to-reach faucet connections), Bucket, Rags or towels
- Permit required
- No
- Contractor recommended
- No
- You will need
- Braided stainless steel supply line (12–24 inches), Adjustable wrench, Basin wrench (for tight spaces), Bucket or towels, Rags for cleanup, Penetrating oil (if connections are stuck)
Materials
- 1 Braided stainless steel supply line with 3/8-inch compression fittings (Measure your run first—common lengths are 12, 16, 20, and 24 inches for sinks; toilets often need 12 inches) — $8-$15
- 2 Replacement rubber gaskets (if not included with new line) (Most quality supply lines come with gaskets pre-installed in the coupling nuts) — $2-$3
Step by step
Kill the Water Flow First
Turn the shutoff valve clockwise until it stops. It's the small oval or round handle on the water line coming out of the wall or floor. Open the faucet or flush the toilet to release pressure and drain any remaining water. Place a bucket or towel under the connection point to catch residual drips.
Tip: If the shutoff valve won't turn or leaks when you try, you'll need to replace that too before proceeding.Loosen and Detach Top
Use an adjustable wrench or basin wrench to loosen the coupling nut where the supply line connects to the faucet tailpiece or toilet fill valve. Turn counterclockwise. If it's stuck, apply gentle pressure and work it back and forth. Once loose, unscrew by hand and pull the line free.
Tip: Hold the tailpiece or fill valve with one hand while loosening the nut to prevent twisting the fixture.Disconnect the Base
Loosen the coupling nut at the bottom end of the supply line where it connects to the shutoff valve. Turn counterclockwise with your wrench. Once loose, unscrew by hand and remove the old line completely. Inspect both connection points for debris or old rubber gasket fragments and wipe clean with a rag.
Tip: If you see corrosion or white mineral buildup around the shutoff valve threads, scrub it off with an old toothbrush before installing the new line.Choose Your New Line
Measure the distance from the shutoff valve to the fixture connection point, adding a few inches for the curved path the line will take. Braided stainless steel supply lines come in standard lengths from 12 to 60 inches. Choose the size that allows a gentle curve without kinking or stretching tight. Check that both ends have the correct fitting size for your connections, typically 3/8-inch compression on both ends for faucets, or 3/8-inch compression to 7/8-inch ballcock for toilets.
Tip: Buy the line slightly longer than you think you need—a gentle loop looks better and stresses the line less than a taut straight shot.Attach the Base First
Thread the coupling nut at one end of the new supply line onto the shutoff valve outlet by hand. Turn clockwise until it's finger-tight and the rubber gasket inside seats against the valve. Then use your wrench to tighten an additional quarter-turn. Don't overtighten—you'll crush the gasket and cause a leak.
Tip: The line should thread on smoothly—if you feel resistance, you're cross-threading and need to back off and start again.Secure the Top Connection
Route the free end of the supply line up to the faucet tailpiece or toilet fill valve, allowing a natural curve. Thread the coupling nut onto the connection point by hand, turning clockwise. Tighten finger-tight first, then add a quarter-turn with your wrench. Again, snug is enough—overtightening damages the gasket.
Tip: Make sure the supply line isn't twisted along its length before final tightening or it will develop stress points.Spot Leaks Immediately
Slowly turn the shutoff valve counterclockwise to restore water flow. Watch both connection points closely for drips or seepage. Let the water run for thirty seconds. If you see moisture, turn off the valve and tighten the leaking connection another eighth-turn. Repeat until dry.
Tip: Dry both connections with a paper towel first, then check after a minute—this makes even tiny leaks immediately visible.Confirm Under Pressure
Wipe down the area and remove your bucket and tools. Run the faucet at full pressure or flush the toilet twice to confirm the line holds under working conditions. Check the connections one more time after ten minutes of use. If everything stays dry, the job is complete.
Tip: Come back in a few hours and check once more—some slow leaks only show up after the connections settle under pressure.
Questions people ask
Do I need to use Teflon tape or pipe dope on supply line connections?
No. Supply lines use compression fittings with rubber gaskets that create the seal. Adding tape or pipe dope interferes with the gasket's ability to seat properly and can actually cause leaks. Just hand-tighten, then snug with a wrench.
How long do braided stainless steel supply lines last?
Replace them proactively anytime you see corrosion, bulging, or moisture around the fittings.
Can I reuse an old supply line if it still looks good?
Don't. Once you've disconnected a supply line, the rubber gaskets have been compressed and won't seal reliably when reinstalled. Supply lines are cheap enough that reusing one is false economy. Always install a new line.
Troubleshooting
The coupling nut won't thread onto the shutoff valve or tailpiece
You likely have the wrong fitting size or are cross-threading. Back off completely, verify the thread size matches, and start again carefully by hand until it catches properly.
Water drips from the connection even after tightening
The rubber gasket is either damaged, missing, or seated incorrectly. Shut off the water, disconnect that end, inspect the gasket, and replace it if torn or flattened. Reinstall and tighten evenly.
The new supply line kinks when routed to the fixture
The line is too short. Forcing a kinked line will eventually cause it to fail. Buy a longer line that allows a gentle curve without stress points.
The old coupling nut is frozen and won't budge
Spray penetrating oil around the threads and wait fifteen minutes. Use two wrenches—one to hold the shutoff valve or tailpiece steady, one to turn the coupling nut. Apply steady pressure, not sudden force.
The shutoff valve itself leaks after you turn the water back on
The valve's internal seal has failed from years of sitting in one position. You'll need to replace the shutoff valve before the supply line replacement will hold.
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