1. To make the syrup, combine all three ingredients in a small sauce pan over medium heat. Bring to a boil and allow the sugar to dissolve. Remove from the heat, cover, and allow to rest for 30 minutes. Remove the sprigs of rosemary and allow to cool. Store in an airtight jar in the fridge.
2. Fill a glass with ice cubes. Squeeze some lime in! Pour in a few tablespoons of rosemary syrup. Pour in a few more tablespoons of vodka. Top with sparkling water. Stir. Drink. Repeat.