In a blender, add in the watermelon, lime juice and granulated sugar. Blend until pureed. You can strain any of the watermelon pulp, but I left it.
Pour the watermelon juice into a large pitcher.
If you were to add any liquor, do it now.
Pour the cold ginger ale into the pitcher and stir. Serve into four glasses and drink immediately. If you plan on drinking it later, hold off on adding the ginger ale until you plan on serving it. Add ice if preferred.