I ferment mine for 24 hours, and then leave it in the fridge for 24 hours before drinking. This is supposed to reduce the sugar further. However, it always has a very slight sweet taste. You could try leaving it in the fridge for 2-3 days before drinking.
One thing to try if you don’t want water kefir is fermented cabbage juice. This is apparently a probiotic, and is made with no sugar.