I'm at 20' on around 50* ground water and cools fine. I pinched the hose about every 5' with a zip tie to make the water turbulent. Don't know if it did anything, but it works well.
You will find copper coils in 20' and 50' lengths... What I did was buy 50' of everything and made two 25' CFC's. I am trying to sell one of them... Interested?
Ended up with 15 feet of 3/8 od tubing made a batch today it worked great took 5.5 gallon from 200 to 75 degrees in about 8 minutes just wish the cheap pump I was using worked as well