Are Catholics allowed to drink coconut water during the hour before they take communion? I know they are not allowed to consume anything but water and medicine during the hour before they take communion. 


  In addition to the fasts mentioned above, Roman Catholics must also observe the Eucharistic Fast, which involves taking nothing but water and medicines into the body for some time before receiving the Eucharist. - Eucharistic Fast (Wikipedia)


But my question is: Is coconut water considered water? Or does it have to be pure Dihydrogen Monoxide?
Have you heard of any catechism lesson FORBIDDING ...


I think your whole question is based on some massive misconception:

As I already wrote in a comment, your question seems to based on the assumption that religion exercise can be done by observing a set of unambiguous rules.

I have often read questions similar to yours in some internet forums where Muslims were discussing. In that religion many faithful seem to have the belief that God wants them to follow a set of unambiguous rules.

In Christian religion (this does not only apply to the Catholics) this is however not the case:

You don't do something because there is some stupid rule somewhere in the canon law or in the catechism. You do something because you love God and you are convinced that God wants you to do something.


So you are convinced that God wants you not to drink anything but water in the hour before the communion?

I think in this case everyone knows that "jelly beans" are not beans, "guinea pigs" are not pigs, ... and "coconut water" is not water.

Why should the catechism explicitly write that? Everyone knows.
You believe the same as the people mentioned in my comment (breakfast before the mass)?

In this case you will deliberately violate Can. 919 CIC because you believe that this rule is not wanted by God.

Why should the church release any kind of text (catechism, CIC rule, ...) intended for that people? They will claim that the text is wrong anyway.


So in none of the two cases a clarification saying that coconut water is something different than water would make any sense.

Why should this clarification be written by anyone?

Because of this reason I doubt that you will find any written text that clarifies that coconut water is not water.