DirectionsIn a small saucepan stir together the water, the sugar, and the creme de cassis, boil the mixture, stirring, until the sugar is dissolved, and simmer it for 5 minutes.
Transfer the syrup to a bowl and chill it, covered, until it is cold.
In a blender puree the watermelon in batches, forcing it as it is pureed through a coarse sieve set over a large bowl, pressing hard on the solids.
Stir into the watermelon puree the syrup, the lime juice, and the bitters and transfer the mixture to an 8-inch-square metal pan.
Freeze the mixture, stirring and crushing the lumps with a fork every 30 minutes, for 2 to 3 hours, our until the granita is firm but not frozen solid.
Scrape the granita with a fork to lighten the texture and serve it immediately.