Step-by-step fix
Step 1: Make sure the supply line is the problem
- Look at the flexible line that runs from the shutoff valve to the faucet, toilet fill valve, or other fixture.
- Dry the line and both connection points with a towel.
- Turn the fixture on briefly, then off, and watch for fresh water at the line, the upper nut, or the lower nut.
- Check for obvious damage like corrosion, bulges, fraying, kinks, or a split hose jacket.
If it works: You confirmed the leak or damage is coming from the supply line or its end connections.
If it doesn’t: If the shutoff valve body, fixture shank, or fill valve is leaking instead, replace or repair that part rather than the supply line.
Stop if:- The shutoff valve itself is cracked, badly corroded, or leaking from the stem or valve body.
- The fixture connection is loose in the sink, tank, or wall and moves when touched.
- You see signs of hidden water damage, rot, or mold inside the cabinet or wall.
Step 2: Shut off water and relieve pressure
- Turn the fixture's shutoff valve clockwise until it stops. Do not force it hard.
- Open the fixture to relieve pressure and let the remaining water drain out.
- Place a bucket under the supply line and lay down a towel under the work area.
- Wipe the fittings dry so you can handle them without slipping.
If it works: Water flow to the fixture has stopped and the line is depressurized.
If it doesn’t: If the shutoff valve will not fully stop the water, shut off the home's main water supply before removing the line.
Stop if:- The shutoff valve will not turn, spins freely, or starts leaking heavily when you operate it.
- You cannot stop water flow enough to disconnect the line safely.
Step 3: Remove the old supply line
- Use one wrench to hold the shutoff valve or fixture fitting steady.
- Use the second wrench to loosen the lower compression nut at the shutoff valve, then loosen the upper nut at the fixture.
- Let the remaining water drain into the bucket.
- Remove the old line and keep it nearby so you can match length, end sizes, and connection style.
If it works: The old supply line is off and you have the old line to compare against the replacement.
If it doesn’t: If a nut is stuck, apply steady pressure while supporting the fitting. If it still will not move, the connected valve or fixture may need separate repair.
Stop if:- A fitting twists in the wall, on the valve, or under the fixture while you loosen the nut.
- The threads are badly damaged or the sealing surface is cracked or misshapen.
Step 4: Match and position the new line
- Compare the new compression fixture supply line to the old one for overall length and both end connections.
- Make sure the new line can reach without stretching, sharp bends, or rubbing on rough edges.
- Thread the upper and lower nuts on by hand first to avoid cross-threading.
- Route the line in a gentle curve rather than a tight loop or kink.
If it works: The new line fits the space and both nuts start by hand cleanly.
If it doesn’t: If the nuts do not thread on easily by hand, stop and recheck the connection size and type before tightening anything.
Stop if:- The replacement line is too short, too long to route safely, or uses the wrong end connection.
- The fitting threads do not match or cross-thread immediately.
Step 5: Tighten the new supply line
- Hold the valve or fixture fitting steady with one wrench.
- Tighten each nut with the other wrench until snug, then give a small additional turn.
- Do not overtighten. Compression-style connections seal by proper fit and moderate tightening, not brute force.
- Wipe both connection points dry so any new leak will be easy to spot.
If it works: The line is secure, supported, and not kinked or twisted.
If it doesn’t: If the line twists while tightening, back off the nut, straighten the line, and retighten while holding the fitting steady.
Stop if:- A nut will not tighten normally, the fitting deforms, or the valve or fixture starts moving in a way that could cause damage.
Step 6: Turn water back on slowly and verify the repair
- Open the shutoff valve slowly while watching the lower connection first, then the upper connection.
- Once the fixture has pressure again, run water for a minute and check both ends with a dry finger or tissue.
- Flush or operate the fixture a few times if applicable, then look again after several minutes.
- Check once more later the same day to make sure the connection stayed dry under normal use.
If it works: Both ends stay dry during use and after the fixture sits under pressure.
If it doesn’t: If a connection seeps, tighten that nut slightly while supporting the fitting, dry it again, and retest. If it still leaks, remove the line and confirm the replacement is the correct type and size.
Stop if:- Water continues leaking after careful retightening.
- The shutoff valve or fixture fitting is now leaking from a different point than before.
- You find water escaping into the wall, floor, or cabinet where you cannot fully inspect it.
Replacement Parts
Repair Riot may earn a commission from qualifying purchases, at no extra cost to you.
FAQ
Do I need thread tape on a compression fixture supply line?
Usually no. Compression-style supply line connections seal at the fitting, not on the threads. Adding tape can interfere with proper tightening.
How tight should the nuts be?
Snug plus a small additional turn is usually enough. Overtightening can damage the fitting or make a leak worse.
Can I reuse the old supply line if it only leaked once?
It is better to replace it. Once a supply line is old, corroded, kinked, or leaking at the connection, replacement is the more reliable fix.
What if the shutoff valve leaks after I touch it?
That usually means the valve itself has a problem, not the supply line. Stop and repair or replace the shutoff valve before continuing.
How do I know which replacement line to buy?
Match the old line's length, both end sizes, and connection style. The new line should reach comfortably without stretching or looping tightly.