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
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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.