It is actually not strange. In English, "white water" refers to a very rapidly moving body of water. (Notice when water flows quickly and splashes against rocks and stones, it creates a white top that is very different from very clear, still water). So if you're moving through life like you are riding a boat on a very rough river, it can be stressful.

The expression "white water" is common & well known. Yes, it is an unusual phrase to use to describe life.