Good question. I would add, why doesn't drinking of this "Living Water" then mean we would never be thirsty again? Jesus said so. Also, Jesus said he was the Bread of Life and those who "ate" this bread would never hunger again, so why does it have to be repeated? Why do people still go eat lunch after Mass?
In John 6 Jesus says that anyone that eats of Him should live forever. Then why to people who take communion in the Catholic church die?
There's a real problem with interpretations that take one sentence in a passage literally and the next figuratively, and then another one metaphorically, all depending on what they want it to say.
In interpreting a passage, there should be at least some consistency in HOW the passage if to be interpreted. If it's to be literal, take ALL of it literally. If it can't all be taken literally without contradicting itself, other Scripture, or making no sense at all, then it's perfectly clear that it ought not to be taken literally, that there's some other way of interpreting it.