Thaks for all this great advice... I read about the restriction "somewhere" while searching for aluminium bottles, and didn't get into it any deeper... so it is very possible that this is simply not true, sorry if I misled anyone... when I get time I'll research this more and get back with my findings... but just a few minutes ago my boss rang and wants me to cycle back to the campsite I work at and fix an acute problem with a lock... so I get an extra 10 miles riding in this lovely swedish spring evening (not to mention the overtime wages

cheers all!