To make rosemary syrup, bring water and ¾ cup sugar to boil in medium saucepan. Remove saucepan from stove; add rosemary sprigs. Let pan sit until syrup has cooled, about 5 minutes then remove rosemary sprigs.
Pour rosemary syrup, grapefruit juice, and vodka into cocktail shaker with ice and shake well.
Wet rims of drink glasses and dip glasses in remaining sugar.
Divide cocktail into glasses and top with lemon-lime soda. Garnish with rosemary and serve
It’s okay to purchase prepackaged grapefruit juice form the store – especially if you’re short on time!