This is best made with freshly squeezed oranges. To save time, look for fresh orange juice that is not made from concentrate.
Combine juice and sugar in a large bowl, stirring until sugar dissolves. Add oranges and water.
Pour orange mixture into the freezer can of an ice-cream freezer; freeze according to manufacturer's instructions. Spoon sorbet into a freezer-safe container; cover and freeze 1 hour or until firm. Garnish with bittersweet chocolate.