Cut half of a small watermelon into cubes and add to blender. Remove the rind & seeds first! Then add fresh lemon juice and blend together.
In cups add sparkling water & top with watermelon lemon juice. I like to do a 1/3 cup sparkling water to 2/3 of a cup of watermelon lemon juice. However, feel free to mix up the ratio so that it's the way you prefer!