But, why?
Except for a few periods of a few months, when I chose to go off caffeine or limited my intake for other reasons, I've been drinking several liters a day of aspartame-and-caffeine-containing drinks since 1996. I've yet to identify any related effects: my teeth aren't great, but haven't been eaten away by acid; I'm overweight, but less than I have been at times since 1990; I don't find dehydration to be a problem. Some of my friends drink similarly large quantities, and none of them have shown any apparent effects, either. This, of course, is mere anecdote, but surely if there were really a serious problem then there'd be an epidemic of some problem easily traced to aspartame, given that millions of people drink liters per day of diet colas and other drinks?
As I am falling into that category (so far drinking diet soda regularly from 16-32 with no noticeable side effects) I do wonder what, if any, problems may come about in later life due to aspartame intake.
I sigh a bit with relief when I read these articles debunking the claims of how bad this stuff is for you. But the doubt still nags at me that there is something not right about taking in so much of this stuff. But then I have the same doubts about too much sugar intake.
The main reasons to avoid sugar from reading I've done in the past are to do with insulin spiking which is indeed a very bad issue, though eating polished rice (white rice), bread etc are all just as bad for that (bread is worse as it also contains sugars). Negative effects on teeth being attributed to sugars are largely false and are more to do with the acidity of the carbonated water used.
There is really nothing wrong with water or tea. Try especially a nice green tea or some other good chinese flavors.
If you must how about use stevia in low amounts for sweetening. It is also not without issues but time has shown that is ok when not consumed overly.