Freeze watermelon cubes in a single layer on waxed paper or parchment. When Cubes are frozen, put into a freezer bag or freezer safe container, removing as much air as possible. Seal and put back in the freezer.
When ready to serve, blend watermelon cubes in a food processor or heavy-duty blender until pureed. Scoop into glasses and serve!
You can a splash of lime juice or some mint syrup for a little something different.