Water kefir soda is very simple to brew, and it is very tasty. Water kefir, also called sugar kefir, is a sweet acidulated drink, a little fizzy, made by fermenting sugars with kefir grains. Most people look at water kefir for its amazing healing qualities, due to the enourmous amount of probiotics. However, this probiotic beverage is one of the best tasting sodas you'll ever drink, if brewed properly.