Is that sentence poorly written? I mean the word elsewhere means in or to another place, and before is a preposition of time, not the place.
2 Answers
The role that water plays elsewhere is a role which it carries out earlier in it's lifecycle.
i.e. it has other roles, and these are not played out here in the topic at hand.
The other roles happen in an earlier part of the sequence of: evaporation; cloud; precipitation as rain or snow, etc.; run-off; capture; bottling.
"before" is a preposition and a conjunction. As a preposition it refers mostly to time, but it can refer to place also in special cases.
In your example "before" is a conjunction, introducing a subordinate clause. See Oald, before, conjunction http://www.oxfordlearnersdictionaries.com/definition/english/before_2