How to Replace a Shutoff Valve Supply Line

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

1. Look under the sink or behind the fixture and find the flexible line running from the shutoff valve to the faucet, toilet fill valve, or appliance connection.
2. Dry the shutoff valve, supply line, and upper connection with a towel.
3. Turn the shutoff valve on briefly if needed and watch where fresh water appears.
4. If water beads on the braided or plastic line, drips from a crimped section, or leaks from the line's end nut, replacing the supply line is the right repair.
5. Turn the shutoff valve fully off before moving on.

If it works: You have confirmed the leak is coming from the supply line or its end connections, not from the valve body or the fixture itself.

If it doesn’t: If the shutoff valve stem, valve body, or the pipe coming out of the wall is leaking, this is a different repair path and the supply line may not solve it.

Step 2: Shut off water and remove pressure from the line

1. Place a bucket or shallow pan under the shutoff valve and supply line.
2. Turn the shutoff valve clockwise until it stops by hand.
3. Open the connected faucet or flush the toilet once to relieve pressure and drain most of the water from the line.
4. Keep the fixture open for a moment until the flow slows to a drip.

Step 3: Remove the old shutoff valve supply line

1. Use a wrench to loosen the nut at the upper end of the supply line while supporting the connected fitting with your free hand if needed.
2. Loosen the nut at the shutoff valve end and let the remaining water drain into the bucket.
3. Remove the old line and compare it to the new one for length, end size, and connector style.
4. Check both connection points for old rubber pieces, debris, or damaged threads, and wipe them clean.

Step 4: Install the new supply line by hand first

1. Route the new line in a gentle curve without sharp bends or kinks.
2. Start the shutoff valve end by hand and turn the nut until it threads smoothly.
3. Start the upper end by hand the same way.
4. Once both ends are hand-threaded, snug each nut with a wrench until secure.
5. Do not use pipe dope or thread tape on typical compression-style supply line nuts unless the line instructions specifically call for it.

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

1. Close the faucet if you opened one, or let the toilet tank begin refilling normally.
2. Turn the shutoff valve on slowly while watching the lower connection first, then the upper one.
3. Wipe both fittings dry and watch for fresh moisture for a minute or two.
4. If you see a small drip at a nut, tighten that connection a little more and check again.

If it doesn’t: If a connection still drips after a small retightening, shut the valve back off, relieve pressure, and inspect for a crooked connection or the wrong replacement line.

Step 6: Verify the repair holds during normal use

1. Run the faucet for a minute, or flush and refill the toilet fully, so the line sees normal pressure and movement.
2. Check the line again with a dry finger or paper towel at both nuts and along the hose body.
3. Look back after 10 to 15 minutes to make sure no slow seep has formed.
4. Remove the bucket and dry the area once you are sure the repair is holding.

If it works: The supply line stays dry during real use and after sitting under pressure.

If it doesn’t: If moisture returns later, shut the valve off and recheck the connection alignment and fit. If the leak source is not the line, inspect the shutoff valve or fixture connection next.