01 - Place the watermelon cubes, cucumber slices, mint leaves, and lime juice in a blender and blend until smooth.
02 - Strain the mixture through a fine mesh sieve into a pitcher to remove pulp, if desired.
03 - Add the sweetener, if using, and stir until dissolved.
04 - Pour in the cold sparkling water, gently stirring to combine.
05 - Serve immediately over ice, garnishing with extra mint leaves and a wedge of lime, if desired.