On a work surface, using a vegetable peeler, remove the zest from half of the lemon. Using a knife, finely chop the zest.
In a small pot, bring 1 cup (250 ml) of the water, the sugar and chopped lemon zest to a boil just until the sugar has dissolved. Pour into a large bowl. Add the remaining water and the lemon juice. Cover and refrigerate for 4 hours.
Pour the chilled mixture into an ice cream maker. Churn for 20 minutes (or according to the manufacturer’s instructions), until it resembles the texture of granita.
Serve in glasses with wide straws. The slushie mixture can be kept chilled in the ice cream maker for up to 1 hour.
Recipes with the "Healthy Pick" stamp have been evaluated by a registered dietitian member of the Ordre professionnel des diététistes du Québec.