Combine all ingredients in a saucepan, and bring to a boil over medium-high heat. Cook for 1 minute or until sugar dissolves; stir constantly. Remove from heat; cool. Pour into a 13 x 9-inch baking dish. Cover; freeze at least 8 hours or until firm.
Remove dish from freezer, and scrape the entire mixture with a fork until fluffy. Store the remaining granita in an airtight container; cover and freeze up to 1 month.