Set a medium mesh strainer over a large bowl.
Split the vanilla bean and scrape the seeds. Keep the pod.
Place lemon slices in the strainer. Add mint rosemary sugar vanilla seeds and the vanilla pod.
Cover the bowl and chill for 2 to 4 hours to let the lemons release their juice.
Press and massage the fruit through the strainer until the bowl holds the lemon juice and melted sugar. Discard the solids.
Stir in the cold water until the sugar fully dissolves.
Pour into a pitcher with ice. Taste and add more sugar or fresh lemon if you like.
Serve cold with extra mint and rosemary. For a fizzy spin swap part of the water with sparkling water just before serving.