Mmmmmm the carbonation in drinks is what keeps the flavor moving around. Well "flat" drinks, or drinks without carbonation in them have a very distinct flavor at the bottom of the bottle/cup.
You're pretty much looking for a Kool-Aid style drink with soda or fruit taste. You could use honey also as a sugar substitute. You could simply make a sache
If you're trying to cut back on acidic drinks because of tooth or intestinal or gastric problems with acidic foods, you can always buy 2 liters, take the cap off and leave it in the fridge.
check these out as well:
http://www.sodastreamusa.com/They sell soda flavors and you use their machine to carbonate your own bottles.
ORRRRRRRRR you could just buy the flavors and add them to your non carbonated water bottles as you wish!!