Step-by-step fix
Step 1: Confirm the supply line is the part that needs replacement
- Look under the sink or behind the fixture and trace the flexible line that runs from the shutoff valve to the faucet, toilet fill valve, or other fixture connection.
- Dry the line and both connection points with a towel.
- Open the shutoff valve briefly if needed and watch for where fresh water appears.
- Replace the line if it is leaking from the hose body, a crimped section, a damaged nut, visible corrosion, or a kink that will not relax.
- If the leak is coming from the shutoff valve body, the fixture itself, or the wall stub-out, this repair will not solve the problem.
If it works: You have confirmed the supply line is the failed part and you know which two ends it connects to.
If it doesn’t: If you cannot tell where the leak starts, dry everything again and wrap each suspect area with a dry paper towel one at a time to pinpoint the first wet spot.
Stop if:- The shutoff valve will not close enough to stop the water.
- The valve body, wall pipe, or fixture connection is cracked, badly corroded, or loose in the wall.
- There is active water damage, mold, or swelling inside the cabinet or wall.
Step 2: Shut off water and remove pressure from the line
- Turn the fixture shutoff valve clockwise until it stops. Do not force it hard.
- Open the faucet or flush the fixture served by that line to relieve pressure and drain off most of the trapped water.
- Place a bucket or shallow pan under the shutoff valve connection and lay down a towel.
- If the fixture has both hot and cold lines, make sure you are working on the correct side before disconnecting anything.
If it works: Water flow from that fixture connection has slowed to a drip and the area is ready for removal.
If it doesn’t: If water keeps running strongly after the valve is closed, shut off the home's main water supply before continuing.
Stop if:- The shutoff valve stem starts leaking heavily when you turn it.
- The valve handle breaks, spins freely, or will not reduce flow.
Step 3: Remove the old supply line
- Use one wrench to loosen the nut on the fixture end of the supply line. If needed, use a second wrench to steady the fixture connection so it does not twist.
- Loosen the nut at the shutoff valve end and let the remaining water drain into the bucket.
- Remove the old line and compare both ends to the replacement.
- Check the shutoff valve outlet and fixture inlet for damaged threads, old rubber stuck to the seat, or debris that could keep the new line from sealing.
- Wipe both connection points clean and dry.
If it works: The old line is out and both connection points are clean and ready for the new line.
If it doesn’t: If a nut is stuck, apply steady pressure and improve your grip rather than jerking the wrench. Recheck that you are turning the nut, not twisting the valve or fixture.
Stop if:- The fixture shank or fill valve starts turning with the nut and you cannot hold it securely.
- Threads are stripped, split, or too damaged for a new line to seat properly.
Step 4: Match and position the new supply line
- Confirm the new line has the same connection type and thread size at both ends as the old one.
- Check that the new line is long enough to reach naturally without being stretched tight and not so long that it has to make a sharp loop.
- Route the line so it will not rub on sharp cabinet edges, get pinched by stored items, or kink when the fixture is used.
- Start each nut by hand first. Turn it several full turns by hand so you know it is not cross-threaded.
If it works: The new line fits the connections and both nuts are started by hand without binding.
If it doesn’t: If the nut will not thread on smoothly by hand, back it off and recheck the end size and alignment before trying again.
Stop if:- The replacement line does not match the old connection type or cannot be routed without a hard bend or kink.
Step 5: Tighten the new line and reopen the shutoff valve
- Tighten the supply line nuts with the wrench until snug. Do not crush, twist, or over-tighten the fittings.
- Hold the shutoff valve or fixture connection steady if needed so the connected part does not rotate.
- Slowly open the shutoff valve and let the line fill under pressure.
- Watch both ends closely for several minutes and wipe each connection with a dry towel or tissue to check for fresh moisture.
- If you see a slight seep at a nut, close the valve and tighten that connection a little more, then test again.
If it works: The line is pressurized and both ends stay dry during the first leak check.
If it doesn’t: If a connection still seeps after a careful small retightening, close the valve, disconnect it, and inspect for a mismatched fitting, cross-threading, or damaged sealing surface.
Stop if:- Water sprays from a connection or the hose body.
- The shutoff valve itself begins leaking from the stem or body during the test.
Step 6: Verify the repair holds during normal use
- Run the faucet fully or operate the fixture several times so the line sees normal pressure and movement.
- Check the line path again to make sure it is not twisting, rubbing, or touching anything hot or sharp.
- Dry the area one last time and come back after 10 to 15 minutes to inspect for slow drips.
- Check again later the same day, especially if the cabinet base or floor was wet before the repair.
If it works: The fixture works normally and the new supply line stays dry during use and after sitting under pressure.
If it doesn’t: If moisture returns, trace it carefully to confirm whether the new line connection needs adjustment or whether the shutoff valve or fixture has a separate leak.
Stop if:- You find water coming from inside the wall, from the valve body, or from another plumbing connection nearby.
Replacement Parts
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FAQ
Do I need thread tape on a fixture supply line?
Usually no. Most fixture supply lines seal with a built-in washer or cone-shaped sealing surface, not with thread tape. Match the connection type and follow the fitting design.
How do I know what replacement line to buy?
Match three things: the connection type on each end, the thread size on each end, and the overall length. Bring the old line with you or measure carefully before ordering.
Can I reuse the old supply line if it only leaked once?
It is better to replace it. Once a supply line has started leaking, kinked, corroded, or damaged fittings can keep causing trouble even if the drip stops for a while.
What if the shutoff valve leaks after I replace the line?
The valve may have its own problem at the stem or body. Replacing the supply line will not fix that. Shut the water back off and plan on repairing or replacing the shutoff valve.
How tight should the supply line nuts be?
Snug and secure, not forced. Start them by hand first, then tighten with a wrench just enough to seal. Over-tightening can damage threads or the sealing surfaces.