In a large saucepan, combine the water, sugar, and ginger. Bring to a boil then simmer for 10 minutes.
Remove from heat to cool to room temperature. (You don't want to add the ginger bug while it's still warm.)
Stir in 3/4 cup of the active ginger bug and the juice of 2 lemons.
Replace the 3/4 cup removed ginger bug with 3/4 cup more water into the ginger bug jar.
Distribute between glass jars with an airtight top. Store in a dark place or on the counter for 3-4 days, until bubbly and carbonated.
Burp the bottles every day to help release gas and keep the glass from exploding (not as scary as it sounds!).
Transfer to the fridge for 2-3 days to help build flavor and slow down fermentation. Enjoy!