In a medium saucepan combine water and sugar. Cook over medium-low heat until sugar dissolves. Cover and chill until cold.
In a large mixing bowl combine melon, orange peel, orange juice, and chilled sugar mixture. Place one-third to one-half of the melon mixture in a blender container or food processor bowl. Cover and blend or process until smooth, stopping and scraping sides as necessary. Place pureed mixture in another bowl. Repeat with remaining melon mixture.
Freeze in an ice-cream freezer according to manufacturers directions. (Or, pour the mixture into a 9x9x2-inch baking pan. Freeze about 3 hours or until frozen around the edges. Spoon into a large chilled bowl. Beat with an electric mixer on high speed until smooth, but not melted. Return to pan. Cover and freeze several hours or overnight.)
To serve, let stand at room temperature for 5 to 10 minutes. Scoop into dessert dishes. Garnish with mint, if desired. Makes 8 servings.