White Residue Sediment In Water Kefir Fermentation

What is the white residue or powder type settled in the bottom of water kefir fermentation jar or ready kefir storing bottle? Is it harmful?

No, it is not harmful. Also it is normal to see powder kind of substance settled in the bottom of the jar or storage bottle. This powder is the natural residue of the live fermentation activity, the taste of the water kefir remains the same. While straining the kefir grains, leave the settlement below and wash the powder away before making a next batch.