Add the Kefir Soda Starter packet OR kefir whey to your juice and stir till dissolved.
Add your lemon and limes and add to a 32-ounce bottle. A funnel helps. (Make sure you use bottles such as Grolsch or Bormioli thick glass bottles. Bottles bought at craft stores can explode.)
Fill the rest of the bottle with water leaving an inch of room at the top.
Allow it to ferment for 3-7 days or until bubbly and fizzy. If your home is 75°F or warmer it will usually take 3-4 days. Colder homes can take 5 days or longer, but you'll need to check it by popping the top and see if it's getting fizzy. It will start to bubble out the top if it does.
When it's done, place it in the fridge right away. You can pour it into a glass and enjoy it right away, but keep it stored in the fridge or it will explode. Consume within 1-2 weeks for the best flavor and most benefit.