In a medium sauce pan, combine two ingredients and stir over medium heat until sugar has dissolved. Bring tea mixture to a light boil. Simmer, stirring occasionally, until reduced to a half of the original amount to create a syrup. This will take 15 minutes or more, depending how thick you want your syrup. Let cool.
For the drink:
In a cocktail shaker, combine rum, simple syrup, bitters, and a sprig of mint. Shake well. Pour into your glass (with or without ice cubes) and top with sparkling water. Garnish with a sprig of mint and enjoy.