It is generally determined by the condo association agreement. However, from basic principle and equity I would say you are correct. The demarcation line for the water pipe is at the turn-off valve in your unit. You have no control over anything past that point, the condo board does. Your best bet is to find a Florida condo attorney and if he agrees with you, have him send a letter to the condo board explaining the facts of life.
Another option, especially if this is or could cause damage to your unit or others, armed with the opinion of the condo board, hire a contractor yourself to fix it. Then send the bill to the condo board and if they don't pay it, sue them at that point. It will be cheaper and simplier for everyone than waiting for damage, etc. and then each side suing the other back and forth over the damages and who is liable.

