In a pitcher or 2 cup measure, combine the grapefruit juice, kombucha and maple syrup. Stir to combine. Fill two glasses with ice and pour the drink over top. If your kombucha isn't naturally effervescent, top each glass off with a little sparkling water. Rub each sprig of rosemary between your hands to help release the oils on the leaves. Pop a sprig in each glass. Adjust sweetness, to taste. Enjoy!