How to Replace Faucet Supply Lines
Updated February 20, 2026
Swap old supply lines for braided stainless steel -- the single best preventive measure against under-sink water damage, and a 20-minute job that could save you thousands.
Overview
Supply lines carry pressurized water 24/7/365. When they fail, they flood the cabinet, the floor, and the rooms below in minutes. Supply line failure is the number one cause of non-weather-related water damage in homes -- insurance companies consistently rank it as a top claim. The fix takes 20 minutes, costs $10-25, and needs one wrench. If your supply lines are rubber, plastic, chrome, or over 10 years old, replace them now with braided stainless steel. This is the single most impactful preventive maintenance you can do to protect your home from water damage.
What You'll Need
Safety First
- Both shut-off valves off before disconnecting. Open the faucet to release pressure. Valves do not fully close? Kill the main.
- Bucket and towels under the connections before you loosen anything. Residual water drains out when you disconnect. Second-floor bathroom? Even a small spill drips through the floor into the room below.
Step-by-Step Instructions
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Turn Off the Water and Disconnect the Old Supply Lines
Valves off, faucet open to drain, bucket in position. Disconnect from the shut-off valves first (lower connections, easier access). Then the faucet tailpieces (upper connections -- basin wrench helps in tight spaces). Let water drain into the bucket. Remove the old lines.
Tip: Note which is hot and which is cold before disconnecting. Hot is left (facing the sink), cold is right. Some lines are color-coded but many are not. Wrong sides will not cause damage, but your faucet handle directions will be reversed. -
Inspect the Shut-Off Valves
With the old lines off, inspect the valve outlets. Check for corrosion, mineral buildup, or thread damage. Clean deposits with an old toothbrush. Cross-threaded or corroded threads will not let the new line seal properly. Old multi-turn gate valve that does not close fully or leaks from the stem? This is the perfect time to swap it for a quarter-turn ball valve.
Tip: While the lines are off, operate each valve -- close and open. A shut-off valve that does not close is a ticking time bomb. If a supply line ever bursts, you cannot stop the water without shutting off the whole house. Replace unreliable valves now. -
Choose and Measure the Correct Replacement Lines
Braided stainless steel only. Flexible, burst-resistant, 10-15+ year lifespan. Match three things: valve-end connection (typically 3/8 inch compression, or 1/2 inch on older valves), faucet-end connection (typically 1/2 inch FIP or 3/8 compression), and length (measure valve to tailpiece, add 2-3 inches for a gentle curve). Too short = stress, too long = kinks. Common lengths: 12, 16, 20, 24 inch.
Tip: Most common combo for kitchen and bath faucets: 3/8 comp x 1/2 FIP. That is how it will be labeled on the package. Not sure? Bring the old lines to the store for matching. -
Install the New Supply Lines
Connect the faucet end first (upper connection). Hand-tighten onto the tailpiece, then a quarter turn with a wrench -- no more. The washer inside the connector makes the seal. Then the valve end (lower connection), same approach. Make sure the line has a gentle curve with no kinks, sharp bends, or tension. Not stretched tight (causes failure), not looped excessively (causes kinks).
Tip: No Teflon tape on supply line connections. These seal with an internal washer, not thread sealant. Tape actually makes it worse -- prevents the nut from compressing the washer properly. -
Test for Leaks
Faucet handle off. Slowly open the hot valve, check both ends for drips. Then the cold valve, same check. Let it pressurize 2-3 minutes, then open the faucet. Run hot and cold for a minute, check all four connections with a flashlight. Dry them off, put a dry paper towel underneath. Check in an hour -- dry paper towel means you are done.
Tip: Drip? Do not just keep cranking. Check that the washer is seated inside the nut (not displaced or missing). Retighten -- but never more than a half turn past hand-tight. Still dripping? Disconnect, inspect washer and threads for cross-threading, reconnect.
Pro Tips
- Replace all supply lines every 10 years proactively, even if they look fine. Rubber and plastic deteriorate internally without visible signs. A $10 replacement prevents a $10,000 water damage claim.
- While you are under the sink, replace the toilet supply line in the same bathroom. Toilet lines are the most neglected and the most common failure point. One braided stainless steel toilet line: $5-8.
- Washing machine hoses too. Second most common cause of water damage after sink supply lines. Braided stainless steel washing machine hoses cost $10-15 per pair. Replace every 5 years.
- Never reuse old supply lines on a new faucet. The rubber washers deform to the old connection and will not seal on a new tailpiece. New lines are cheap insurance.
- Water leak detector ($15-30, battery-powered) under the sink is smart insurance. It alarms when it detects water. Can mean the difference between a towel cleanup and a full-floor replacement.
When to Call a Pro
This never requires a professional. Call a plumber if the shut-off valves need replacing (especially on galvanized pipes), if the faucet tailpiece threads are damaged, or if you find water damage in the cabinet that needs assessment.