Step-by-step fix
Step 1: Make sure the supply line is really the problem
- Dry the shutoff valve, supply line, and fixture connection with a towel.
- Watch closely while the water is on and look for the highest point where fresh water appears.
- If the drip starts from the braided or plastic line, from a crimped section, or from one of the line nuts, replacing the supply line is the right next step.
- If water is coming from the valve stem, valve body, wall, or the fixture itself, the leak source is somewhere else.
If it works: You have confirmed the supply line or its end connection is the source of the leak.
If it doesn’t: If you cannot tell where the leak starts, dry everything again and wrap each area with a dry paper towel one at a time to pinpoint the source before buying parts.
Stop if:- Water is coming from inside the wall or cabinet rather than from the exposed line.
- The shutoff valve is badly corroded, loose, or leaking from the valve body.
- The cabinet, floor, or wall shows swelling, rot, mold, or other hidden water damage.
Step 2: Shut off the valve and prep the area
- Turn the nearby shutoff valve clockwise until it stops.
- Open the faucet or fixture served by that line to relieve pressure and drain the remaining water.
- Place a bucket or bowl under the connection and lay down a towel to catch drips.
- Take a quick photo of the old line routing so you can copy the same path with the new one.
If it works: The line is depressurized and the area is ready for removal.
If it doesn’t: If the fixture keeps running strongly after the valve is closed, the shutoff valve may not be holding. You may need to shut off water to the home before continuing.
Stop if:- The shutoff valve will not close enough to stop the flow.
- The valve handle feels like it may break or the valve starts leaking heavily when you turn it.
Step 3: Remove the old compression supply line
- Use one wrench to steady the shutoff valve if needed and another to loosen the supply line nut.
- Disconnect the line from the fixture side and then from the shutoff valve side, letting the remaining water drain into the bucket.
- Remove the old line carefully so you do not bend or stress the valve or fixture connection.
- Compare both ends of the old line to the new one before installing anything.
If it works: The old line is out and you have confirmed the new line has matching connections.
If it doesn’t: If the new line does not match both ends exactly, stop and exchange it for the correct size and connection type.
Stop if:- A fitting is seized so tightly that the valve or fixture starts twisting with it.
- The valve or fixture connection is cracked, stripped, or badly corroded once the old line is removed.
Step 4: Install the new line without twisting or kinking it
- Route the new line in a gentle curve with no sharp bends, kinks, or stretching.
- Start the nut on the shutoff valve by hand and turn it several full turns so you know it is not cross-threaded.
- Start the nut on the fixture side by hand the same way.
- Once both ends are hand-threaded correctly, tighten them with a wrench until snug. If you use a second wrench to steady the valve, keep the valve from twisting.
- Do not force the line into position. If it is too short or the bend is too tight, use the correct length instead.
If it works: The new line is installed squarely, with both ends snug and the tubing routed cleanly.
If it doesn’t: If a nut will not thread smoothly by hand, back it off and realign it before tightening again.
Stop if:- The line must be bent sharply to reach either connection.
- Threads feel damaged or the nut will not start straight by hand.
Step 5: Turn the water back on slowly and check for leaks
- Close the faucet or fixture you opened earlier.
- Turn the shutoff valve on slowly while watching both ends of the new line.
- Wipe each connection dry, then watch and feel for fresh moisture for several minutes.
- If you see a small seep at a nut, tighten that connection slightly and recheck.
- Run the fixture normally for a minute, then inspect the line again under pressure.
If it works: The line stays dry with the water on and while the fixture is running.
If it doesn’t: If a connection still seeps after a small retightening, shut the valve back off, remove the line, and check for the wrong fitting, cross-threading, or a damaged mating surface.
Stop if:- Water sprays from a connection or the leak gets worse when pressure returns.
- The shutoff valve itself begins leaking during the test.
Step 6: Confirm the repair holds in real use
- Use the fixture a few times over the next several hours as you normally would.
- Check the line again after the cabinet or floor has dried so even a small new drip is easy to spot.
- Make sure the line is not rubbing on sharp edges or being pinched by stored items under the sink or behind the fixture.
- Keep the old line until you are sure the replacement is holding and the fit is correct.
If it works: The new compression supply line stays dry during normal use and the original leak is gone.
If it doesn’t: If moisture returns later, trace the highest wet point again. The leak may be from the shutoff valve, fixture shank, or another nearby connection rather than the new line.
Stop if:- You find repeated leaking even with the correct line installed and properly tightened.
- There are signs of ongoing water damage beyond the exposed connection area.
Replacement Parts
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FAQ
How do I know what replacement supply line to buy?
Match three things: the length, the fitting size at the shutoff valve, and the fitting size at the fixture. Bring the old line with you if possible, or measure and compare both ends carefully before ordering.
Can I reuse the old supply line if I tighten it more?
It is better to replace a line that is leaking, kinked, cracked, or corroded. Tightening may slow a drip for a short time, but it does not fix a damaged line.
Do I need thread tape on a compression supply line?
Usually no. Compression-style and many supply line connections seal at the fitting, not on the threads. The important part is using the correct matching connection and tightening it properly.
How tight should the new line be?
Start both ends by hand, then tighten until snug and leak-free. If a connection seeps, tighten a little more and recheck. Avoid cranking down hard, which can damage the fitting.
What if the shutoff valve leaks after I replace the line?
That points to a different repair. If the valve leaks from the stem or body, the supply line was not the only problem and the valve may need service or replacement.