ARCORA FAUCETS
If you’ve found a puddle in your base cabinet, a kitchen sink supply line leaking is the most common culprit — and the good news is it’s usually the cheapest and easiest plumbing leak to fix yourself. The supply line is the short flexible hose that carries pressurized water from the shut-off valve under your sink up to your faucet’s inlet. When it drips, it’s rarely the faucet’s fault; it’s almost always the connection or the hose. Below, I’ll walk you through exactly where the leak is coming from, how to stop it in the next 20 minutes, when to tighten versus replace, and how to pick a supply line that won’t do this again.
Why is my kitchen sink supply line leaking in the first place?
Your supply line is leaking for one of four reasons: a loose connection nut, a worn-out rubber washer or gasket, a corroded/cracked hose, or over-tightening that split the seat. That’s it — 95% of supply line leaks trace back to one of those four. Water under pressure will find any weak point, and a supply line has exactly two connection points (bottom at the valve, top at the faucet) plus the hose body itself, so there aren’t many places to check.
The most frequent offender is simply a nut that has vibrated loose over months of use, or one that was never quite tight enough after an install. The second most common is an aging rubber washer inside the connection that has gone hard and brittle. If you have older chrome-plated copper or plastic supply lines, the third cause — a pinhole crack or a corroded fitting — becomes much more likely. And ironically, the fourth cause is people cranking the nut too hard, which cracks the compression seat or the plastic ferrule and makes the leak worse.
- Loose nut: drip appears right at the threaded connection; often stops with a gentle snug.
- Bad washer/gasket: drip persists even when the nut feels tight — the rubber has failed.
- Cracked or corroded hose: water beads along the hose body or at a rusty fitting, not just at the nut.
- Over-tightened / split seat: leak got worse after you tightened it — you’ve cracked something.
How do I tell if the leak is the supply line or the faucet itself?
Dry everything completely, then run your finger along the supply line connections and the faucet base while the water is on — whichever spot feels wet first tells you the source. A supply-line leak lives below the sink, at the flexible hoses and shut-off valves. A faucet leak shows up above the counter (dripping spout, water pooling around the faucet base or handle). This 30-second test saves you from replacing the wrong part.
Here’s the reliable method: shut off, dry the entire area under the sink with a paper towel, then place a fresh dry paper towel under each connection point. Turn the water back on, run the faucet for a minute, then turn it off and check the sink cabinet 10–15 minutes later. The paper towel that’s wet points you straight to the leaking joint. If both the top and bottom connections stay dry but the hose middle is damp, the hose body itself has failed and must be replaced — you can’t patch a supply line.
One more clue: if water only appears when the faucet is running, it’s likely the top (faucet-side) connection or the hose. If water leaks even when the faucet is off, it’s the bottom (valve-side) connection or the shut-off valve, because that side is always under pressure. If you’re not sure whether the drip above the counter is related, our guide on what a leaking faucet really means helps you decode where the water is actually coming from.
How do I stop a leaking kitchen sink supply line right now — step by step?
Turn off the shut-off valve, place a bucket and towel underneath, then hand-tighten the leaking nut and give it a quarter-turn with an adjustable wrench — that stops most supply line leaks in under five minutes. If tightening doesn’t fully seal it, you replace the line. Here’s the full sequence:
- Shut off the water. Turn the football-shaped shut-off valve under the sink clockwise until it stops. Two valves (hot and cold)? Close both. No under-sink valve? Shut off the main.
- Relieve the pressure. Open the faucet to drain the residual water in the line, then close it.
- Protect the cabinet. Slide a shallow bucket or old towel under the connections to catch drips.
- Snug the leaking nut. Hand-tighten first, then use an adjustable wrench for a quarter to half turn — no more. Hold the valve body steady with a second wrench so you don’t twist the valve.
- Test. Reopen the shut-off, run the faucet a minute, and check with a dry paper towel. Dry? You’re done.
- Still leaking? Replace the line. Unscrew both ends, take the old hose to the hardware store to match length and fitting size, and install a new braided stainless line (see the next section).
A word of caution that catches a lot of DIYers: do not keep cranking a leaking nut tighter and tighter. If a quarter-turn past hand-tight doesn’t seal it, more force will crack the seat or crush the washer and turn a small drip into a spray. At that point, replacement is the right call, not more torque. If your shut-off valve itself is weeping or won’t close, that’s a separate repair — a job that overlaps with replacing a washing machine faucet valve, since the shut-off mechanism works the same way.
Should I replace the supply line or just tighten it — and how long do these last?
Replace the line (don’t just tighten) if the hose is more than 8–10 years old, if you see any bulge, corrosion, kink, or crack, or if tightening the nut doesn’t stop the leak on the first try. Tightening is fine for a fresh, healthy braided line that simply worked loose; replacement is the smart move for anything aging or damaged, because a $10 hose failing at 60 PSI can flood a kitchen.
Supply lines are cheap insurance. A braided stainless-steel line costs less than a takeout lunch and takes 15 minutes to swap, while a burst line while you’re at work can cause thousands in water damage. Insurance companies actually cite failed supply lines and washing-machine hoses as a leading source of household water-damage claims. If yours is the old chrome-copper or gray plastic type, upgrading to braided stainless is one of the highest-value 10-minute jobs in your house.
| Supply Line Type | Typical Lifespan | Burst Risk | Cost | Best For |
|---|---|---|---|---|
| Braided stainless steel | 8–10+ years | Low | $8–$15 | Almost everyone — the modern default |
| PEX / reinforced polymer | 5–8 years | Low–Medium | $5–$10 | Tight spaces, plastic fittings |
| Chrome-plated copper | 5–7 years (kinks) | Medium | $6–$12 | Rigid, exposed runs where looks matter |
| Vinyl / plastic (old style) | 3–5 years | High | $3–$6 | Not recommended — replace when found |
My rule of thumb: if you’re already under the sink fixing a leak and the line is more than five years old or anything but braided stainless, just replace it while you’re in there. It costs a few dollars and saves you a repeat trip.
What size and length supply line do I actually need for a kitchen faucet?
For most kitchen faucets you need a 3/8-inch compression fitting on the valve end and a 1/2-inch or faucet-specific connector on the faucet end, in a 20-inch length — but always match your old line rather than guessing. Take the failed hose to the store and compare it side by side; supply lines are sold by connection type on each end and by length, and getting either wrong means another trip.
The two ends often differ. The bottom (valve) side is usually a 3/8-inch compression nut that fits standard angle stops. The top (faucet) side depends on your faucet — many modern kitchen faucets, including pull-down models, come with their own 3/8-inch or 1/2-inch female connectors, and some have captive supply hoses already attached so you only connect the bottom. Length matters too: too short and it strains the connections; too long and it kinks. A 16–20 inch line covers most standard-height cabinets.
- Valve end: most commonly 3/8″ compression (fits typical angle-stop shut-offs).
- Faucet end: 1/2″ FIP or a faucet-specific connector — check your faucet’s spec sheet.
- Length: 12″, 16″, 20″, or 24″ — measure valve-to-inlet with a little slack, no tight stretch.
- Material: braided stainless steel with an EPDM inner tube is the reliable default.
If you’re replacing the whole faucet at the same time — which is common once you’re already under there — it’s worth thinking about the faucet itself. A quality pull-out or pull-down model usually ships with better supply hoses; see our breakdown of the best pull-out single-handle kitchen faucet setups and the long spout reach kitchen faucets for deep or double-bowl sinks to see what connectors different designs use.
How do I install a new supply line so it never leaks again?
Hand-thread both nuts first to avoid cross-threading, snug them with a wrench only a quarter-turn past hand-tight, and — this is the key — do not use plumber’s tape on compression or captive-gasket connections, because those seal on a rubber washer, not the threads. Over-tightening and mis-applied tape cause more re-leaks than anything else.
Braided stainless lines have a built-in rubber gasket (a cone or flat washer) at each end that does the sealing. Start each nut by hand and turn several full rotations by fingers alone — if it won’t spin freely, you’re cross-threaded, so back off and realign. Only once it’s finger-tight do you bring in the wrench for that final quarter-turn. Then run the water and watch the connections for a full minute; a properly seated line is dry immediately, not “drying up over a day.”
Two pro habits that prevent callbacks: keep the line’s natural loop gentle — no sharp kinks that stress the fitting — and don’t reuse an old crush washer. If your connection uses threaded pipe rather than a gasket (rare on modern flexible lines but common on rigid fittings), then and only then does a few wraps of PTFE plumber’s tape belong. For the finish and hardware side of faucet work, the same careful-torque principle applies when you change bathroom faucet knobs — snug, not gorilla-tight.
When is a leaking supply line actually a bigger plumbing problem?
If the water is coming from the shut-off valve body (not the supply-line nut), if you see green corrosion or white mineral crust building up, or if the leak returns within days of a proper repair, the issue is upstream of the supply line and may need a plumber. A simple hose swap won’t fix a failing valve or a corroded stub-out.
Watch for these red flags: a shut-off valve that won’t fully close or drips from its stem, active corrosion on copper stub-outs, or a musty smell and swollen cabinet floor that signals the leak has been slow and ongoing. Persistent moisture also invites mineral buildup and rust on nearby fittings — if you’re already seeing that, our guides on fixing a rusted faucet and removing hard water stains without wrecking the finish will help you clean up and prevent a repeat. But a weeping valve stem or a leak that survives a correct hose replacement is your signal to call a pro before water damage spreads.
FAQ
Can I use plumber’s tape to stop a supply line leak?
Usually no. Braided and compression supply lines seal on a rubber gasket or metal ferrule, not on the threads, so plumber’s tape does nothing there and can even hold the nut slightly off-seat. Only use PTFE tape on tapered threaded pipe connections. If a gasketed line still leaks after a proper quarter-turn snug, replace the line — don’t try to tape it.
How much does it cost to fix a leaking kitchen sink supply line?
DIY, it’s about $8–$15 for a new braided stainless line plus 15 minutes of your time. If you hire a plumber just for the supply line, expect roughly $100–$200 with the trip charge and labor. Because the part is so cheap and the job so quick, most homeowners handle this one themselves — it’s genuinely beginner-friendly.
How tight should a supply line nut be?
Hand-tight plus a quarter to half turn with a wrench — no more. These connections seal on a soft gasket, so gorilla-tightening crushes the washer or cracks the seat and makes leaks worse. If it still weeps after a quarter-turn, the washer or hose has failed and needs replacing, not more force.
Why is my supply line leaking only when the faucet is on?
A leak that appears only while running usually sits at the faucet-side (top) connection or in the hose body, where flow briefly raises pressure and flexes the line. A leak present even with the faucet off is on the valve side, which stays pressurized. Use the dry-paper-towel test on each end to pinpoint it, then tighten or replace that connection.
How often should I replace kitchen sink supply lines?
Braided stainless lines last 8–10+ years; older plastic or chrome-copper lines should be swapped every 5 years or at the first sign of stiffness, corrosion, or a kink. Any time you replace a faucet or work under the sink, it’s smart to install a fresh braided line while you’re already there — it’s a few dollars of cheap insurance against water damage.
Can a leaking supply line cause serious water damage?
Yes. Even a slow drip can rot a cabinet base, feed mold, and warp flooring over weeks, and a full burst under 50–80 PSI household pressure can release gallons per minute. Failed supply lines are a top source of home water-damage insurance claims, which is exactly why replacing an aging line proactively is worth the ten minutes.
About the author: This guide was written by the Arcora product team, drawing on hands-on faucet installation and repair experience across thousands of kitchen and bathroom fixtures. About Arcora: arcorafaucet is a dedicated faucet and bathroom-fixture brand engineering kitchen faucets, shower systems, and sink hardware built to last. Our faucets and supply components are pressure-tested and built to meet cUPC / NSF standards for lead-free drinking-water safety, and many models carry a limited lifetime warranty on finish and function. When you buy a replacement supply line or faucet from us, it ships tested and ready to install.