Replace the faucet supply line or the whole faucet?

A standard 3/8-inch compression fitting at the shutoff valve doesn’t by itself confirm that a replacement line will fit. The faucet-side connection may use a different thread, a proprietary hose, or a permanently attached connector. Verify both ends against the faucet manufacturer’s specification, and inspect the shutoff valve for corrosion or damaged threads before disconnecting the old line.

If the faucet is otherwise sound and the valve operates cleanly, replacing only the corroded supply line is usually the lower-risk repair. Replace the faucet as well if its attached hose is corroded, the faucet-side fitting is damaged, or access is difficult enough that repeating the work soon would be a concern. Shut off the water, relieve pressure, and use a backup wrench so the shutoff valve isn’t twisted.

Check the shutoff valve before disturbing a corroded supply line. It should close fully and reopen without seeping at the stem or compression outlet; an older valve can begin leaking once the line is moved, even if the original leak was only at the connector. If it does not shut off reliably, factor valve replacement into the repair, and use a backup wrench so loosening the 3/8-inch compression nut does not twist the valve.

Put a shallow pan or several towels under the connection before loosening a 3/8-inch compression nut, even after the shutoff is fully closed.

- Water can remain in the flexible line and faucet passage, then drain as soon as the fitting separates.
- A pan also makes it easier to spot seepage from the shutoff outlet or valve stem after the line is moved.
- If the shutoff does not hold fully, use the main water shutoff before proceeding.

For a faucet and attached connection that are otherwise sound, replacing only a corroded supply line is still generally the lower-risk repair. Catching the leftover water and checking the valve can keep a small repair from becoming cabinet damage.

The pan and towels are especially useful for catching the water left in the line, but the leak check shouldn’t stop when the cabinet looks dry. After installing the replacement, run the faucet briefly, then dry both connections completely. Recheck them after several minutes and again later, since a slow seep at a compression fitting may take a little time to show up. A dry paper towel wrapped around the joint makes a tiny leak much easier to spot than a quick glance.

A dry paper towel after a brief test is useful, but a slow seep may not show immediately. For anyone replacing a supply line, dry both connections completely, run the faucet, and recheck with a paper towel after several minutes and again later.

Avoid testing the connections by twisting or trying to move them. If a leak appears at a compression joint, shut off the water and make only a very small adjustment to the nut, using a backup wrench on the valve or fitting so it is not twisted. Overtightening can damage the fitting or ferrule.

The 3/8-inch size at the shutoff doesn’t tell you how the replacement line seals. Check the connector instructions to confirm whether it uses a washer or a compression ferrule, and don’t assume the old sealing parts can be reused.