Combine water and sugar in a small saucepan. Bring to a boil, reduce heat, and simmer 5 minutes. Remove from heat, and let cool completely. Stir in juices.
Pour mixture into freezer container of a 4-quart hand-turned or electric freezer. Freeze according to manufacturer's instructions. Pack freezer with additional ice and rock salt; let mixture stand in freezer 1 hour before serving.
Scoop sorbet into individual bowls. Garnish, if desired. Serve immediately.