Adjustable wrench
Use it for: To loosen and tighten the supply line nuts at the shutoff valve and faucet.
Shop adjustable wrenchesFaucet plumbing repair
How to Replace a Faucet Cold Supply Line
To replace a faucet cold supply line, shut off the cold water, relieve pressure, remove the old line from the shutoff valve and faucet, install a matching new line without twisting it, then turn the water back on and check closely for leaks.
This is a good DIY repair when the cold line is leaking, kinked, corroded, or blocked and the shutoff valve and faucet body are still in good shape. The main job is matching the new line correctly and tightening the connections enough to seal without damaging them.
Before you start: Match the line length, both end sizes, and the faucet connection style before ordering. Bring the old line with you if you are unsure.
Safety first
- Work with the cold shutoff valve fully closed before disconnecting the line.
- Support the shutoff valve with a wrench if needed so you do not twist the pipe in the wall.
- Use a bucket and towels because even a depressurized line will spill some water.
- Do not force mismatched fittings or overtighten connections that are not threading on cleanly.
Tools you may need
Basin wrench
Use it for: Helpful if the faucet connection is tucked up behind the sink where a regular wrench will not fit well.
Shop basin wrenches
Bucket or small pan
Use it for: To catch the water left in the line when you disconnect it.
Find a drip pan or bucket
Towels or rags
Use it for: To protect the cabinet floor and wipe fittings dry during leak checks.
Shop absorbent shop towels
Flashlight
Use it for: To see the shutoff valve, faucet connection, and any slow drips under the sink.
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Step-by-step fix
Step 1: Make sure the cold supply line is really the problem
- Run the faucet and note what is happening: a drip under the sink, weak cold flow, no cold flow, or visible corrosion on the line.
- Look under the sink with a flashlight and find the cold side supply line running from the cold shutoff valve to the faucet.
- Dry the line, valve, and nearby fittings with a towel, then turn the cold water on briefly and watch for fresh moisture.
- Confirm the leak or restriction is coming from the line itself or its end connections, not from the shutoff valve body, faucet body, or drain parts.
If it works: You have identified the cold supply line as the failed part or the most likely cause of the problem.
If it doesn’t: If the shutoff valve is leaking from its stem or body, or the faucet is leaking above the sink, fix that part instead before replacing the line.
Stop if:
- The shutoff valve will not close fully.
- The valve, wall pipe, or cabinet area shows heavy corrosion, rot, or active damage.
- You cannot tell where the water is coming from after drying and rechecking.
Step 2: Shut off the cold water and prep the area
- Turn the cold shutoff valve clockwise until it stops.
- Open the faucet to the cold side to relieve pressure and let the remaining water drain out.
- Place a bucket or pan under the shutoff valve and lay towels in the cabinet.
- If the hot and cold lines are crowded together, take a quick photo so you can reconnect the new line the same way.
If it works: The cold line is depressurized and the work area is ready for a controlled removal.
If it doesn’t: If water keeps flowing strongly from the cold side, the shutoff valve is not holding and needs attention before you continue.
Stop if:
- The shutoff valve does not stop the water enough to work safely.
- Turning the valve causes the pipe at the wall to move or flex noticeably.
Step 3: Remove the old cold supply line
- Use one wrench to steady the shutoff valve if needed and another to loosen the supply line nut at the valve.
- Let the remaining water drain into the bucket.
- Move to the faucet end and loosen that connection as well. Use a basin wrench if access is tight.
- Pull the old line out and keep it oriented the same way so you can compare length, end sizes, and connection style.
- Wipe both connection points clean so the new line can seat properly.
If it works: The old cold supply line is out and you can clearly compare it to the replacement.
If it doesn’t: If a nut is stuck, apply steady pressure and improve your tool angle rather than forcing the valve or faucet to twist.
Stop if:
- The shutoff valve or faucet shank starts turning with the nut.
- Threads are damaged, split, or badly corroded on the valve or faucet connection.
Step 4: Match and install the new supply line
- Compare the new line to the old one for overall length, nut size, and faucet-end connection type.
- Route the new line in a smooth curve without a sharp bend or twist.
- Start the faucet-end connection by hand first so you do not cross-thread it.
- Start the shutoff-valve connection by hand next.
- Tighten each connection snugly with a wrench. If you need to hold the valve body steady, use a second wrench so you do not stress the pipe coming from the wall.
- Make sure the line is not rubbing hard against sharp cabinet edges or kinked behind the sink.
If it works: The new cold supply line is installed squarely and routed cleanly.
If it doesn’t: If the nuts will not thread on smoothly by hand, back them off and recheck the fit before tightening again.
Stop if:
- The replacement line does not match the old line's connection type or size.
- A fitting only catches a few threads or feels cross-threaded.
- The line must be forced into place to reach the connections.
Step 5: Turn the water back on and check for leaks
- Close the faucet.
- Slowly open the cold shutoff valve and watch both ends of the new line as pressure returns.
- Wipe each connection dry, then watch for several minutes for beads of water or a slow drip.
- If you see a minor drip at a connection, tighten that connection a little more and dry it again before rechecking.
- Run the faucet on cold for a minute, then shut it off and inspect the line and fittings one more time.
If it works: The line stays dry under pressure and during normal faucet use.
If it doesn’t: If a connection still drips after a careful small retightening, shut the valve back off and recheck the fit, thread alignment, and whether you bought the correct line.
Stop if:
- Water is spraying or leaking heavily from a connection.
- The shutoff valve now leaks from its stem or body after being turned back on.
Step 6: Confirm the repair holds in real use
- Use the faucet normally on cold and mixed temperature settings several times.
- Check under the sink again after 10 to 15 minutes and once more later in the day.
- Feel around the cabinet floor and the line connections for any hidden moisture.
- Leave the area dry so any new drip will be easy to spot over the next day or two.
If it works: Cold water flow is normal and the cabinet stays dry, confirming the replacement solved the problem.
If it doesn’t: If cold flow is still weak or missing with a dry new line, the restriction may be in the shutoff valve, faucet inlet, or faucet cartridge instead of the supply line.
Stop if:
- You find recurring moisture that is not coming from the new line.
- The faucet still has the same cold-water problem even though the new line is installed correctly and not leaking.
Replacement Parts
Find a faucet cold supply line on Amazon
Match the line length, both end sizes, and the faucet connection style before ordering. Bring the old line with you if you are unsure.
As an Amazon Associate I earn from qualifying purchases. Repair Riot may earn a commission at no extra cost to you.
Verify the repair
- The new line matches the old line's length and both connection types.
- Both ends threaded on by hand before final tightening.
- The line is not kinked, twisted, or stretched tight.
- No drips appear while the valve is open, while the faucet is running, or after the faucet is shut off.
- The cabinet floor stays dry after normal use.
FAQ
Do I need thread tape on a faucet supply line?
Usually no on the supply line nuts themselves. Most faucet supply line connections seal at a washer or built-in gasket, not on the threads. Match the replacement correctly and tighten it properly instead of adding tape unless the fitting specifically calls for it.
How do I know which side is the cold supply line?
On most faucets, the cold shutoff is on the right side when you are facing the sink. If you are unsure, turn on the faucet and close one shutoff valve at a time to confirm which line feeds the cold side.
Can I replace just the cold supply line and leave the hot one alone?
Yes, if only the cold line is leaking, kinked, or blocked and the hot line is still in good condition. If both lines are the same age and show wear, many homeowners replace both while access is open.
What if the new line is a little longer than the old one?
A little extra length is usually fine if the line can make a smooth loop without kinking or rubbing sharply. Do not use a line that is too short or one that has to be bent hard to fit.
Why is there still weak cold water after I replaced the line?
If the new line is dry and installed correctly, the problem may be elsewhere, such as a clogged shutoff valve, debris at the faucet inlet, or a faucet cartridge issue. The line may not have been the root cause.