Seltzer water is available in numerous flavored varieties, which is why a lot of people have now claimed to be 'addicted' to it. If you are concerned about calories you may be happy to know that it does not contain any calories, nor does it contain any additives such as artificial sweeteners or phosphoric acid, thereby making it safer in comparison to other sodas. On the other hand, it is possible that the flavored versions of seltzer water may have some calories along with sodium, artificial flavors, and sugar.