Boil the water in a large pot, then turn off the water and add the tea bags and the sugar. Stir to completely dissolve the sugar.
Let the tea completely cool to room temperature (this will take several hours or overnight), then remove the tea bags and transfer it to a gallon jar, leaving enough room at the top for the SCOBY and kombucha starter.
Add the kombucha starter to the tea, then add the SCOBY to the jar. It may float and it may sink, either way is ok.
Cover the jar with cheesecloth and a rubber band and put it in an out of the way spot away from direct sunlight.
The kombucha will take anywhere from 1-3 weeks to fully ferment. It will taste slightly vinegary and will have formed a new baby SCOBY on the surface of the kombucha.
Reserve the SCOBY and 2 cups of kombucha to start a new batch.
You can bottle and refrigerate the fermented kombucha and enjoy it as is, or you can do a flavored second ferment in order to create a delicious, probiotic-rich soda.
Notes
A SCOBY is a living organism, and it can be damaged, so make sure your hands are clean before feeding your kombucha.
By the time you consume kombucha, the SCOBY has consumed most of the caffeine and sugar.
The kombucha starter does not have to be an exact measurement. Just make sure that the SCOBY is completely submerged in the starter.
If the SCOBY breaks apart in the process, it's ok. It will grow back as it feeds on the sweet tea!
With each fermentation process, you should gain a new, thin SCOBY across the top of your kombucha.
The baby SCOBY will be much lighter in color than the rest and darken over time with each fermentation process. This means your SCOBY is alive and well!
Store SCOBY(s) in a large glass bowl with enough kombucha starter to cover. Place a cloth over the top of the bowl so that no dust or insects get in.