Water kefir uses sugar to feed the grains (as opposed to milk kefir which uses the milk sugar – lactose – to feed the grains).
I have made water kefir with dextrose in order to limit the fructose content but it wasn’t successful (I think you need much larger quantities & even then, it’s a poor substitute to sugar). Using sugar I left mine to ferment until it was bordering on sour in order to avoid ingesting any fructose but I still had tremendous bloating issues. I also have the same issues when consuming saurkraut (made as recommended above). I have concluded that my system is reacting to certain types of bacteria. I find that I can tolerate Lactobacillus Acidophilus fine but the bifidobacterium species affect me. Since I cannot control the bacteria species growing in kefir, kombucha or saurkraut, so I no longer consume them (a real shame).
I now make homemade yogurt with a culture that excludes bifidobacterium and I take a L. Acidophilus supplement.
We are all different!