What is causing the minor leak in flex supply line under sink?

Question

I had new shutoffs and new flex supply lines installed by a professional plumber a few months ago. Today, I installed a new faucet because mine was very old and starting to fail. I installed everything successfuly however I am now noticing an extremely minor leak in my cold water supply line. Basically, I can run the water for 5 minutes and nothing would happen but when I shut off the water at the faucet, a few seconds later, I get a tiny drop of water build and drip from the area I outlined below.

I didn't disconnect the supply lines from the shutoff values when installing the new facuet so I figured that maybe I losened it slightly by mistake during installation. I tightened it as much as I could, just to be safe, but the problem seems to still be happening.

Any ideas?

Answer 1

The joint that you are pointing to in your picture is a compression joint. Usually a little bit more tightening of the nut will stop it. If you are absolutely sure you can't get another 1/8 or 1/4 turn on the nut, then simply shut off the valve and replace the hose. The Teflon tape mentioned in the previous answer is necessary on new hose threads, but has nothing to do with a leak in the joint you are leaking from.

Answer 2

I'd shut the water off to that tap, unscrew the joint and apply some PTFE tape to the thread before reattaching the flex pipe.

Over the years I've found that joints that were previously OK can start weeping when the system is disturbed in some way, so this isn't unusual.