Is this the same for bottle of water? "...eine Flasche Wasser..."
yes, for all contents, and for all kinds of containers
Why not " I will open a wine bottle"?
Because when putting 'eine Flasche' before the 'Wein' or 'Wasser' it will turn to a bottle of wine. If you want to say a wine bottle, it would be 'Weinflasche'
Why there is "eine", *Flasche is masculine, isn't it?
no, "Flasche" is feminine