Quote Originally Posted by SnappyPix
Unless this is used in pure racing circles, I must admit that I've never heard water bottles referred to as bidons in general conversation in the UK.

Incidentally, found this very good site with a glossary of terms:
http://www.torelli.com/raceinfo/glossary.html
It was used in a book (_French Revolutions_) written by a British guy, definitely not a racer, so that's what made me think it might be generally used there. Oh, well...