Cut up the watermelon into chunks. Put in the blender and blend until you have 5 cups of juice. Add the remaining ingredients and blend until smooth. Allow to sit until the foam subsides.
Clear space in the freezer for a large baking dish. Pour the mixture into the dish and set it flat in the freezer. Set the timer for one hour.
After one hour, break up any ice with a fork. Set the timer for 30 minutes and rake with a fork until you have fluffy snow. (May take about 4 hours.) Here's a video of me making prickly pear granita using this method. If you watch closely, you'll see Buddy Girl appear a few times:
Store in an airtight freezer container.
Notes
Per serving:
54 calories
0 g fat
0 g saturated fat
0 g monounsaturated fat
0 g polyunsaturated fat
0 g trans fat
0 g cholesterol
2 mg sodium
150 mg potassium
12 g carbohydrate
0 g fiber
5 g sugars
0 g protein
1 Weight Watchers Points Plus
Additional notes:
The bigger the dish = the more area = the faster this will freeze.
You can make this without an ice cream maker. If you have an ice cream maker and want to use it, add a little more tequila. You'll end up with a sorbet, and the tequila will help keep it from freezing solid if you put it back in the freezer.