1Heat the pomegranate juice in a small saucepan over medium heat until steam rises from the surface and a few bubbles have formed around the perimeter of the pan, about 5 minutes. Remove from heat.
2Add the sugar and stir until it has dissolved and the mixture is no longer cloudy, about 5 minutes. Stir in the orange-flower water (if using) and let the syrup cool to room temperature, about 30 minutes. Refrigerate until chilled, about 1 hour.
3Pour the chilled pomegranate syrup, club soda, and lime juice into a 6-cup pitcher and stir gently to combine (stirring too vigorously will deflate the fizz). Float lime slices in the pitcher. Serve over ice with additional lime slices.