Step 1: Prepare the rosemary syrup by combining 1/2 cup sugar and 1/2 cup water in a small saucepan over medium heat.
Step 2: Add 2 large sprigs of fresh rosemary to the saucepan and bring to a gentle simmer, stirring until the sugar is fully dissolved.
Step 3: Remove the saucepan from the heat and let the syrup steep for at least 10 minutes to allow the rosemary flavor to infuse.
Step 4: Strain the syrup into a clean glass jar, discarding the cooked rosemary sprigs, and allow it to cool completely in the refrigerator.
Step 5: In a large pitcher, combine the 2 cups of fresh orange juice with 4 tablespoons of the cooled rosemary syrup (adjust to your preferred sweetness).
Step 6: Fill four tall glasses with ice and pour the orange mixture until the glasses are about two-thirds full.
Step 7: Top each glass with chilled sparkling water and stir gently with a long spoon.
Step 8: Garnish your orange rosemary drink recipe with a fresh rosemary sprig and an orange slice before serving immediately.