Place cubed watermelon in a blender, and process until smooth, working in batches if needed. Pour mixture through a strainer into a large, clean pitcher. Discard any solids caught in the strainer.
Add Ginger Syrup and lime juice, stirring to combine. Sample the mixture, and add more Ginger Syrup or lime juice to taste (if needed). Stir in the sparkling water. To serve, pour into a short glass over ice, and garnish with a sprig of mint. Want to make this a boozy spritzer? Just add vodka!
* If you don't want to make Ginger Syrup at home, there are a number of options available for purchase online.