In a medium saucepan, combine the water and sugar over medium heat. Stir until the sugar is completely dissolved, then remove from heat and let cool.
In a mixing bowl, combine the Mandarin orange juice, lemon juice, and orange zest. Mix well.
Once the sugar water has cooled, add it to the Mandarin orange mixture and stir until fully combined.
Pour the mixture into an ice cream maker and churn according to the manufacturer's instructions until it reaches a soft-serve consistency.
Transfer the sorbet to an airtight container and freeze for at least 4 hours or until firm.
Before serving, let the sorbet sit at room temperature for about 5 minutes to soften slightly.