Use a crusher to crush the watermelon and mint leaves and release the juices in a pitcher. Alternatively, blend the cubed watermelon in a blender, until smooth, working in batches if needed. Pour mixture through a strainer into a large, clean pitcher. (You may discard the solids as they will be without flavor)

Add concentrated ginger syrup and lime juice, stirring to combine. Stir in the sparkling water. Taste for sugar, ginger, or lime and add according to preference. Pour into a glass over ice, and garnish with a sprig of mint. Want to make this boozy? Just add a splash of vodka or tequila!