To make mint ice cubes, add finely chopped mint to two ice cube molds.
Fill with water and place in freezer until solid.
In a medium saucepan, bring 2 cups water and 1 cup sugar to a boil.
Stir until sugar dissolves completely then pour into a pitcher.
Stir in lemon juice and additional 4 cups of water.
Add watermelon to a blender or food processor and blend until smooth.
Push the watermelon though a mesh strainer and discard watermelon "meat". This is optional if you like a chunkier fruit filled lemonade add all the watermelon.
Add watermelon juice to the pitcher and stir.
Chill until ready to serve.
To serve: fill glasses with a hand full of mint ice cubes and pour chilled watermelonade on top. Add a straw and top with a thin wedge of watermelon.