Combine the water, sugar, and limoncello in a medium saucepan. Bring to a boil, stirring frequently, until sugar is dissolved. Add the lemon juice and chill for 2 hours or overnight.
Freeze in an ice cream machine according to manufacturer's directions, about 30 minutes. Transfer to a sealable container and freeze for at least 2 hours.
To serve, scoop into a glass, pour a shot of limoncello over and serve.
Calories: 189kcal, Carbohydrates: 41g, Protein: 1g, Fat: 1g, Saturated Fat: 1g, Sodium: 4mg, Potassium: 31mg, Fiber: 1g, Sugar: 40g, Vitamin C: 12mg, Calcium: 4mg, Iron: 1mg