01 - Place the watermelon cubes, cucumber slices, mint leaves, and lime juice in a blender.
02 - Blend on high speed until completely smooth and no large chunks remain.
03 - Pour the blended mixture through a fine mesh sieve into a pitcher to remove pulp for a smoother texture. Skip this step if you prefer a thicker consistency.
04 - Stir in the erythritol or chosen sweetener until fully dissolved. Taste and adjust sweetness as desired.
05 - Pour in the cold sparkling water and stir gently to combine while preserving some carbonation.
06 - Pour over ice-filled glasses and garnish with additional mint leaves and a lime wedge if desired.