As is pointed out in the post, in Aus "Lemonade" = Sprite, 7up, etc. Slightly lemony and sparkling. Schweppes also sells it and actually calls it "Lemonade". Unflavoured is called "soda water". Schweppes sells that, too. Tonic Water (also usually from Schweppes) is soda water with quinine.

I don't think we have our own term for the non-sparkling American version. But we kinda understand it, bascially courtesy of American media.

Wade.