1. Combine water and sugar in a small sauce pan over low heat and stir until sugar is dissovled.
2. Add lemon and stir until mixed well.
3. Let sit until it cools to room temperature.
4. Transfer mixture to a tupperware container and refrigerate for at least 4 hours or overnight.
5. Remove mixture from refrigerator and process in ice cream maker following manufacturer's instructions until granita is slushy with little chunks of soft ice, 20-30 minutes.