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