Mix water and sugar and bring to a boil in a small cooking pot.
Turn off the heat; add tea, cover, and steep about 15 minutes.
Strain the tea into a glass container. Allow the tea to cool to body temperature.
Place the SCOBY and starter in the tea.
Cover with a cloth and store in a warm spot, ideally 70º to 85ºF (21º to 29ºC).
After a few days to 1 week, depending on temperature, you will notice a skin forming on the surface of the kombucha. That's the new mother (SCOBY). Taste the liquid. It will probably still be sweet. The longer it sits, the more acidic it will become.
Once the kombucha reaches the acidity you like, start a new batch with some of the mature kombucha as starter. Store the rest in the refrigerator for consumption or proceed with a second fermentation.
With every batch of kombucha fermentation, a new mother (SCOBY) will be born. Store extra SCOBYs in mature kombucha in the SCOBY hotel.
Notes
This recipe is loosely based on the book Wild Fermentation by Sandor Ellix Katz.