Add chopped ginger to a saucepan and add water. Bring to a boil then turn down to a high simmer. Simmer for 10 minutes.

Remove saucepan from the heat and stir in sugar until it dissolves.

Strain liquid in saucepan into a 4-cup measuring cup or bowl using a mesh strainer to catch the ginger.

Allow mixture to cool to room temperature and then add ginger bug and stir well.

Decant mixture into a jar and put on a lid and allow to ferment for 2 - 6 days. Loosen lid each day to release fermentation gas that will build up in jar. Once the desired level of carbonation and flavor have been achieved, refrigerate.