There has been 100's of reports on carbonated water and drinks. Some have said it is bad for you, and others have said it is perfectly fine, and in many cases good for you. All by medical doctors at respected universities.
I would guess that it is fairly safe, I mean, the amount of CO2 or bodies deal with in a day is tremendously more then the amount from a drink or too. That is my opinion.
But in health, just like everything else, the key to health is moderation.
I too am very healthy and athletic, and let me suggest to you some other options that are sweet tasting, to add variations to your diet.
There are various fruit juices that are virtually sugar free (~10-15 calories per serving). Tropicana makes an excellent Fruit Punch. Minute made makes an excellent 15 calorie lemonade.
You can also find Low sugar orange/tangerine fruit juices.
There is even a sugar free orangeade in a can; which is absolutely wonderful and convenient.
Not only do all these taste good, and low calorie to not ruin your diet, but they also contain vitamins and minerals.
Some of the V8 splash fruit juices are great, and again ~15 calories per serving, with lots of vitamins and minerals.
You should look around your local grocery store at the juices (both in the refrigerated case typically near dairy and on the isle).
There are lots of very sweet tasting drinks, that are ultra low calorie and have lots of vitamins and minerals you need; which can spice up your diet while loving it.