Cut open the watermelon into two and remove all the seeds from both sides. Do not worry about the small whitish seeds as they will blend well.
Cut the watermelon into small slices and place them inside a blender.
Blend. Consider using the Nutribullet blender for its ability to liquify the watermelon very fast. Nonetheless, any other blender will serve you well.
Once you have blended the watermelon, mix equal amounts of the sparkling water and the blended watermelon juice.
Compress the 3 lemons and obtain their juices.Add the lemon juices to the mixture of watermelon juice and sparkling water, and there you have your watermelon refresher.