2 bunches of mint (2 ounces), 12 small sprigs reserved, the rest coarsely
chopped (with stems)
8 cups chilled sparkling water
Using a vegetable peeler, remove the zest from 8 of the limes, leaving behind as much of the bitter white pith as possible. Juice all 13 limes.
In a medium saucepan, combine the water with the sugar, chopped mint and lime zest strips and bring to a simmer. Cook over moderate heat for 5 minutes. Remove from the heat and let cool for 30 minutes. Strain the syrup into a large pitcher. Stir in the lime juice and sparkling water. Serve in ice-filled glasses, garnished with the mint sprigs.