How to Replace Faucet Supply Lines
Faucet supply lines are the flexible hoses that carry water from the shutoff valves under your sink to the faucet above it — and they are one of the most common sources of household water damage when they fail. Learning how to replace faucet supply lines is a straightforward job that takes about 30 minutes per faucet, costs less than $30 in parts, and can prevent a burst line from flooding your kitchen or bathroom. This guide covers when to replace them, which type to buy, and the exact steps to install new braided lines without a single drip.
What Supply Lines Do — and When to Replace Them
Every sink, toilet, and faucet in your home has supply lines connecting it to the water supply. Under a bathroom or kitchen sink, you will see two lines — one hot, one cold — running from the shutoff valves on the wall or floor up to the faucet connections. They are under full household water pressure 24 hours a day, which is why a failure is so destructive: a burst supply line can release gallons of water per minute, and if nobody is home, it can flood a room before anyone notices. Supply lines should be replaced every 8–10 years as preventive maintenance, and sooner if you see any warning signs. Look for bulging or kinking in the hose, corrosion or green deposits on the fittings, cracks or fraying in the outer braid, dampness or mineral deposits around the connections, or any rust on the shutoff valve itself. If your home still has the old gray plastic (polybutylene) or plain rubber supply lines, replace them now — those types are notorious for bursting without warning. Braided stainless steel lines are the modern standard and the ones you want. Also replace the lines any time you install a new faucet, since the old lines rarely match the new faucet's connections and reusing them is a false economy. While you are under the sink, check the shutoff valves too: if a valve is stiff, corroded, or will not fully shut off, replace it at the same time, since you already have the water off.
Choosing the Right Replacement Lines
Buying the correct supply lines starts with measuring. The most important number is the length: measure from the shutoff valve outlet to the faucet connection, and buy a line that is a few inches longer than the measurement so it can curve gently without kinking or pulling tight. Common lengths are 12, 16, 20, and 24 inches, and a line that is slightly too long is fine — you can loop it in a gentle curve. A line that is too short is useless and dangerous, since it will be under tension. Next, match the connection sizes. Most bathroom and kitchen faucets use a 3/8-inch compression fitting at the shutoff valve end and a 1/2-inch or 3/8-inch connection at the faucet end, but there are variations, so check your faucet's manual or bring the old line to the store for comparison. Buy braided stainless steel lines from a reputable brand — they cost $8–$15 each in 2026 and are worth every penny over the $3–$5 vinyl alternatives. The stainless braid resists bursting, kinking, and punctures, and the brass fittings hold up far better than plastic ones. Avoid the cheapest no-name lines; a supply line is not a place to save four dollars. Buy both the hot and cold lines at the same time so they match in age and condition, and pick up a roll of Teflon tape and a small tube of pipe joint compound while you are at the store, though most braided lines seal with a rubber washer and do not need sealant on the compression end.
Tools and Materials You Will Need
This job needs very little equipment, and you probably own most of it already. You will need an adjustable wrench and a pair of tongue-and-groove pliers for loosening and tightening the fittings, a small bucket and several old towels to catch the water that drains from the lines, and a flashlight or headlamp, since the space under a sink is dark. Have the new braided supply lines ready, plus Teflon tape in case any threaded connection needs it. A basin wrench is helpful if the faucet connections are hard to reach from above, though most supply lines connect under the sink where a regular wrench fits. Our guide to essential plumbing tools for homeowners lists the full starter kit if you are building one. Before you start, confirm you know where the shutoff valves are for this fixture and that they work — turn each valve clockwise until it stops, then open the faucet and confirm the water stops flowing. If a shutoff valve does not stop the water, do not start the job: you will need to shut off the main water supply and replace the faulty valve first. Lay a towel in the bottom of the cabinet to protect the wood and to soak up drips, and keep your phone nearby in case you need to look up your faucet model mid-job.
Step-by-Step: Replacing the Supply Lines
Start by turning off both shutoff valves under the sink, turning them clockwise until they stop. Open the faucet to release pressure and drain the lines, then place the bucket under the connections. Disconnect the old lines at the shutoff valve end first, using the adjustable wrench to loosen the compression nut while holding the valve steady with the pliers — this prevents you from twisting the valve or the pipe behind it. Have the bucket ready, because water will drain out of the line. Then disconnect the other end at the faucet, which may be a compression nut or a threaded connection depending on the faucet. Pull the old line out and compare it with the new one to confirm the length and fittings match. Before installing the new line, inspect the shutoff valve outlet and the faucet inlet for corrosion or damaged threads, and wipe them clean. Install the new line at the faucet end first, hand-tightening the nut, then snug it with the wrench — about a quarter-turn past hand-tight is enough for a compression fitting with a rubber washer, and overtightening can crack the fitting or crush the washer. Route the line in a gentle curve with no kinks or sharp bends, then connect the other end to the shutoff valve the same way. Repeat for the second line. Double-check that the hot line goes to the hot valve and the cold line to the cold valve — they are usually marked, and mixing them up means the faucet handles will be reversed. Finally, make sure neither line is touching a sharp edge, a hot pipe, or the garbage disposal, since vibration and heat shorten the life of the hose.
Testing for Leaks the Right Way
Testing is the most important part of the job, and it should not be rushed. Turn the shutoff valves back on slowly, one at a time, and watch both connections on that line closely. Dry the fittings with a towel first so that any new moisture is obvious. Check the faucet-end connection and the valve-end connection, and run your finger around each nut — even a tiny bead of water means the connection needs attention. If you see a drip, turn the water off, tighten the nut another eighth of a turn, and test again. Do not overtighten; if a second small tightening does not stop the drip, turn the water off, disconnect the line, and check the rubber washer inside the nut — it may be missing, damaged, or seated crookedly. Once both lines are dry at full pressure, open the faucet and let the water run for a minute to flush any air and debris from the lines, then check the connections one more time. Leave a dry paper towel under each connection and check it again after an hour, and once more the next morning. A slow leak that only appears under sustained pressure is easy to miss in the first five minutes, and catching it the next morning is far better than discovering it a week later when the cabinet floor is swollen. If the lines stay dry after 24 hours, the job is done. For related repairs under the sink, see our guide on how to install a P-trap.
Common Mistakes to Avoid
Most supply line failures after replacement come from a handful of avoidable mistakes. The biggest is overtightening the compression nut, which crushes the rubber washer or cracks the fitting — hand-tight plus a quarter-turn is enough. The second is cross-threading: if a nut does not turn smoothly by hand for the first few threads, stop, back it off, and start again straight. Forcing a cross-threaded nut will strip the threads and ruin the fitting. The third mistake is buying a line that is too short, which puts the hose under tension and stresses both connections every time the cabinet vibrates or the faucet moves. Measure twice and buy a line with a few inches to spare. The fourth is reusing old washers or old supply lines when installing a new faucet — new lines are cheap, and old ones are the ones most likely to fail. The fifth is forgetting to check the shutoff valves: if a valve is corroded or will not fully close, replacing the line above it is pointless, because the valve itself is the next failure waiting to happen. And the sixth is skipping the 24-hour leak check. A connection can look dry for an hour and still weep slowly under pressure, so the paper-towel test the next morning is not optional. Avoid these six mistakes and your new supply lines should last a decade or more.
Cost, Lifespan, and When to Call a Pro
Replacing faucet supply lines yourself is one of the cheapest high-value jobs in home plumbing. The parts cost $16–$30 for a pair of braided stainless steel lines, plus a few dollars for Teflon tape if you need it, and the job takes 30–45 minutes for a first-timer. A plumber would charge $150–$300 for the same job, so the savings are real. Braided stainless steel lines last 8–10 years in normal use, and some manufacturers rate them for longer, but the 10-year replacement rule is cheap insurance against a burst line. Replace them sooner if you notice any of the warning signs listed above, and always replace them when you install a new faucet. Call a plumber if the shutoff valves are corroded, seized, or leaking, since replacing a valve often means working on the supply pipe itself and may require soldering or a compression fitting in a tight space. Also call a pro if the faucet connections are corroded solid, if the supply pipes are galvanized steel that crumbles when touched, or if you find water damage, mold, or a soft cabinet floor while you are under the sink — those are signs of a bigger problem. For help deciding which jobs are worth doing yourself, read our guide on DIY vs hiring a plumber, and browse the full DIY plumbing hub for more step-by-step repair guides.