Put watermelon chunks into food processor and process until mixture looks soupy.

Place a strainer over an empty bowl. Pour watermelon mixture into strainer, and strain out all of the juices, pressing on the solids. You should have 4 cups of strained watermelon juice. Discard the solids.

Stir in lime juice and simple syrup.

Serve over ice and garnish with fresh limes, watermelon, and a mint leaf.