In a small saucepan over medium heat, combine the water and sugar, and boil until the sugar dissolves, about 1 minute.
Remove from heat and allow the syrup to completely cool.
Once cool, stir in the watermelon juice and lemon or lime juice.
Pour the mixture into a 9x5 metal baking pan.
Freeze until firm (about 4 hours), stirring with a fork every thirty minutes for the first 3 hours. This is important, don’t skip this step.
Store covered in the freezer for up to 3 months.
