How to Replace a Shutoff Valve Supply Line

Step 1: Confirm the supply line is the part that needs replacement

1. Dry the shutoff valve, supply line, and the fixture connection with a towel.
2. Open the shutoff valve and run the fixture briefly so the line is under normal pressure.
3. Watch for water forming on the braided or smooth line, at the nut where it meets the shutoff valve, or at the nut where it meets the fixture.
4. Check that the valve body itself is not leaking from the stem, handle area, or the valve-to-pipe connection in the wall or floor.
5. Measure the old line length and note both end connections so you can buy the same style replacement.

If it works: You have confirmed the leak is coming from the supply line or its end seals, and you know what replacement line to use.

If it doesn’t: If the valve body, stem, or pipe connection is leaking instead, this is the wrong repair path and the shutoff valve or piping needs attention.

Step 2: Shut off the water and relieve pressure

1. Turn the shutoff valve clockwise until it stops.
2. Open the connected faucet or fixture to relieve pressure and drain the line.
3. Place a bucket or shallow pan under the shutoff valve and line.
4. Keep a towel nearby for the small amount of water that will spill when the line comes off.

Step 3: Remove the old supply line

1. Use one wrench to hold the shutoff valve steady if needed, and another to loosen the supply line nut at the valve end.
2. Disconnect the other end of the line from the fixture or appliance connection.
3. Lower the line into the bucket and let the remaining water drain out.
4. Compare the old line to the new one for length, nut size, and connection style before installing anything.

Step 4: Install the new shutoff valve supply line

1. Start the new line on the shutoff valve by hand so the threads engage cleanly.
2. Start the other end by hand at the fixture connection.
3. Make sure the line is not kinked, sharply bent, or pulled tight. A gentle curve is better than tension.
4. Tighten each connection snugly with a wrench after hand-threading. Do not force the nuts past snug just to make them feel extra tight.

Step 5: Turn the water back on and check for leaks

1. Close the faucet or fixture you opened to relieve pressure.
2. Open the shutoff valve slowly and watch both ends of the new line.
3. Wipe each connection dry, then check again after a minute for fresh moisture.
4. If you see a small drip at a nut, tighten that connection a little more and recheck.

If it doesn’t: If a connection still drips after a careful slight retightening, shut the water back off and inspect for a mismatched line, damaged threads, or a poor seal at the connection.

Step 6: Verify the repair in normal use

1. Run the fixture for a minute or two and then shut it off.
2. Check the line again while the water is flowing and again after the fixture is off.
3. Feel under both connection nuts with a dry finger or tissue to catch slow seepage.
4. Look back after 15 to 30 minutes to make sure no delayed drip has formed in the cabinet or on the floor.

If it works: The supply line stays dry during use and after sitting under pressure, so the repair held.

If it doesn’t: If moisture returns later, shut the valve off and recheck the connection fit and line type. If the line is dry but the valve or pipe is wet, the leak source is elsewhere.