How can I start fermenting lemonade at home?

To start fermenting lemonade at home, mix fresh lemon juice, sugar, and water in a glass jar. Add a small amount of active yeast or a starter culture. Cover the jar with a cloth and let it sit at room temperature for 1-2 days, stirring occasionally. Taste the lemonade to check for desired level of fermentation, then strain and refrigerate before serving.