Wash and sterilize a quart-sized jar. Warm 1 cup of the filtered water and dissolve the sugar in it. Let cool to room temperature. Transfer to the jar, add kefir grains, and remaining filtered water. Cover jar with the cloth or coffee filter and secure with jar ring or rubber band.

Place jar in a warm corner or cupboard away from direct sunlight.

Allow to ferment for 24-48 hours; the water kefir will ferment more quickly in warmer temperatures and during the summer. Bubbles will be visible rising from the bottom to the top of the jar as soon as a few hours, but the longer it ferments, the bubblier it will become.

Strain out the water kefir grains to make another batch. The water kefir can be consumed at this point, or bottled for a second fermentation.

For second fermentation, transfer the water kefir to a bottle with a swing top. (Glass jars and bottles are preferred, but plastic soda bottles can also be used.)

For flavored water kefir, add ¼ cup of pure fruit juice or diced fruit into the bottle then add the water kefir. Seal the bottle tightly. Let ferment an additional 24-48 hours. Crack the seal of the bottles at least once a day to prevent pressure building up. The kefir is ready to drink. Store in the refrigerator.