Adjustable wrench
Use it for: To loosen and tighten the supply line nuts at the shutoff valve and faucet connection.
Shop adjustable wrenchesUnder-sink plumbing repair
How to Replace an Under Sink Shutoff Valve Supply Line
To replace an under sink shutoff valve supply line, shut off the home water if needed, remove the old line, match the new line by length and connection size, install it without twisting, then reopen the water slowly and check for leaks.
This is usually the right repair when the flexible line is dripping at a crimp, has corrosion, kinks, or keeps leaking even after you snug the connection. If the shutoff valve body itself is leaking, the valve may need separate repair or replacement.
Before you start: Match the line length, end sizes, and connection type before ordering.
Safety first
- Support the shutoff valve body while loosening or tightening the line so you do not twist the pipe in the wall.
- Use the main water shutoff if the under-sink valve will not close fully.
- Keep towels and a small pan under the work area because even a drained line usually holds some water.
- Do not force corroded fittings that are making the valve or pipe move.
Tools you may need
Channel lock pliers
Use it for: To hold the valve body steady so you do not twist the pipe coming out of the wall.
Shop tongue and groove pliers
Small bucket or pan
Use it for: To catch the water left in the line when you disconnect it.
Find a drain pan or bucket
Old towel 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 back side of the valve and faucet connections under the sink.
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Step-by-step fix
Step 1: Make sure the supply line is really the problem
- Empty the cabinet so you can see both ends of the line clearly.
- Dry the shutoff valve, supply line, and faucet connection with a towel.
- Turn the shutoff valve on and off, then watch where fresh water appears.
- Look for drips from the braided or smooth flexible line itself, from a crimped end, or from a damaged nut or washer area.
- If water is coming from the valve stem, valve body, or the pipe at the wall, note that the leak is not limited to the supply line.
If it works: You have confirmed the leak or damage is on the supply line or at one of its end connections.
If it doesn’t: If you cannot tell where the leak starts, wrap each area with a dry paper towel one at a time and check which one gets wet first.
Stop if:
- The shutoff valve body is cracked, badly corroded, or leaking from the wall connection.
- The pipe coming out of the wall moves when touched.
- The cabinet, wall, or floor shows swelling, rot, mold, or long-term hidden water damage.
Step 2: Shut off water and relieve pressure
- Close the under-sink shutoff valve by turning it clockwise.
- If the valve will not close fully or keeps dripping heavily, shut off the main house water instead.
- Open the faucet served by that line to relieve pressure and let residual water drain out.
- Place a bucket or pan under the valve and lay towels in the cabinet.
If it works: Water flow has stopped or slowed to a small residual drip, and the line is safe to remove.
If it doesn’t: If water keeps running strongly from the faucet with the shutoff closed, use the main water shutoff before continuing.
Stop if:
- The shutoff valve handle will not turn and feels like it may break.
- The valve leaks much worse when you try to close it.
Step 3: Remove the old supply line
- Use one tool to hold the shutoff valve body steady and a second tool to loosen the supply line nut.
- Disconnect the line from the shutoff valve first, then disconnect the other end from the faucet or fixture connection.
- Let the remaining water drain into the bucket.
- Lay the old line out straight and note its length, end sizes, and whether each end is the same or different.
- Check the sealing surfaces on both connections and wipe away mineral buildup or debris.
If it works: The old line is off, and you know the replacement length and connection style you need.
If it doesn’t: If a nut is stuck, apply steady pressure while supporting the valve body. If it still will not move, the connection may be too corroded for a simple line swap.
Stop if:
- The shutoff valve or supply stub starts twisting with the nut.
- Threads are stripped, crushed, or too corroded to seal reliably.
Step 4: Match and position the new supply line
- Compare the new line to the old one before installing it.
- Confirm the new line reaches both connections without stretching, sharp bends, or a tight loop.
- Start each nut by hand to avoid cross-threading.
- Route the line so it does not rub on sharp cabinet edges and does not kink when the cabinet contents are put back.
If it works: The new line fits the space and both nuts thread on by hand smoothly.
If it doesn’t: If the line is too short, too long to route cleanly, or the nuts do not start easily by hand, stop and get the correct replacement.
Stop if:
- You have to force the nut to catch the threads.
- The only way to make it fit is with a severe bend or twist in the line.
Step 5: Tighten the connections without twisting the line
- Hold the shutoff valve body steady with pliers or a second wrench.
- Tighten the shutoff-valve end snugly with the adjustable wrench.
- Tighten the faucet or fixture end snugly as well.
- Keep the line body from spinning as you tighten so the hose stays relaxed.
- Do not overtighten. The goal is a firm seal, not crushed threads or distorted fittings.
If it works: Both ends are snug, the valve body stayed still, and the line is not twisted or kinked.
If it doesn’t: If a nut keeps turning without feeling snug, back it off and inspect the threads and fit again before reopening the water.
Stop if:
- A fitting cracks, deforms, or will not tighten normally.
- The valve or pipe at the wall begins to move.
Step 6: Restore water slowly and prove the repair holds
- Close the faucet if you left it open for draining.
- Open the shutoff valve slowly while watching both ends of the new line.
- Wipe each connection dry, then watch for several minutes for fresh moisture.
- Run the faucet normally for a minute, then shut it off and check again.
- Come back after 10 to 15 minutes and do one more dry-hand or paper-towel check around both fittings and under the line.
If it works: The line stays dry during pressurizing, while the faucet is running, and after the water sits under pressure.
If it doesn’t: If a connection seeps, gently snug that nut a little more while supporting the valve body, then dry it and test again. If it still leaks, remove the line and recheck the fit and connection type.
Stop if:
- Water sprays, drips steadily from the valve body, or leaks from a wall connection.
- The cabinet or wall starts getting wet from a source other than the new line.
Replacement Parts
Find an under sink shutoff valve supply line on Amazon
Match the line length, end sizes, and connection type before ordering.
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 faucet runs normally with the shutoff valve fully open.
- Both supply line connections stay dry during use and after the faucet is turned off.
- The new line is not kinked, stretched, or rubbing on a sharp edge.
- No new dripping appears from the valve body, wall connection, or cabinet floor.
FAQ
How do I know if I need the supply line or the shutoff valve itself?
If the flexible line is wet along its body, leaking at a crimp, or damaged, replace the supply line. If water comes from the valve handle, valve body, or where the valve connects to the pipe at the wall, the valve is the problem.
Can I reuse the old supply line?
It is better to replace it once removed, especially if it is older, kinked, corroded, or leaking. A new line is inexpensive compared with water damage from a repeat leak.
Do I need thread tape on a supply line connection?
Usually no for standard supply line nuts that seal with their own built-in washer or cone-style seal. The important part is using the correct connection type and tightening it properly.
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 bend without kinking or rubbing. Do not force a tight loop or sharp bend just to fit it in the cabinet.
Why does it still drip after I replaced the line?
The most common causes are the wrong end size, cross-threading, a damaged sealing surface, or a leak that is actually coming from the shutoff valve instead of the line.