Heat 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. (Do not boil.) Remove from heat. Add sugar and stir until it has dissolved and the liquid is no longer cloudy, about 5 minutes. Stir in lemon juice and orange-flower water and let the syrup cool to room temperature, about 40 minutes. Transfer to a container with a tightfitting lid and refrigerate for up to 1 month.