In a medium saucepan over high heat, combine water and sugar; cook until sugar dissolves. Cool to room temperature and set aside.
In a large mixing bowl, combine melon, orange zest, juice, and sugar mixture. Place half of melon mixture in a blender or food processor and puree until smooth. Pour into bowl of an ice-cream maker.
Repeat with remaining melon mixture. Then freeze in ice-cream maker according to manufacturer’s directions.
Scoop frozen sorbet into dessert dishes and garnish with mint leaves if desired.