Cut the watermelon into small cubes, removing any seeds.
Place the watermelon cubes in a blender or food processor.
Add the sugar, lime juice, and water to the blender.
Blend the mixture until smooth.
Taste and adjust sweetness if needed.
Pour the mixture into a shallow container.
Cover the container and freeze for 1 hour.
Stir the mixture to break up ice crystals.
Continue freezing for another 3 hours, stirring every hour.
Scoop the sorbet into bowls and garnish with mint leaves.