In a blender puree watermelon pieces, then strain through a fine mash sieve to extract as much liquid as you can..

In a large glass,combine mint, simple syrup and lime juice with the back of a wooden spoon.Add ice. Pour in watermelon juice and sprite or soda water. Stir to combine.

Serve mojito garnished with lime wedges or a slice of watermelon or as per your choice..