Most sparkling flavoured waters have citric acid in so are not allowed.
I think there are a few that are ok.
Check out the 'what can we drink on exante' sticky up the top.
Tesco and sainsburys do 1.5 litre bottles of still flavoured waters though and they are allowed (not the lemon and lime one from tesco though)
I have the tesco strawberry and the apple one and they are both lovley, really help with the water intake.