Bring 3 cups water and 1 cup sugar to a boil in a saucepan, stirring mixture constantly. Pour into a large bowl; add lime juice and next 4 ingredients. Cover and freeze 8 hours.
Process frozen mixture in a blender or food processor until slushy. Dip margarita glass rims into water; dip rims in sugar. Spoon granita into glasses.
Note: For a nonalcoholic version, omit liquors, and add 1/2 cup fresh orange juice.
The Coastal Living Cookbook
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