Add water and sugar in a medium saucepan, then heat until the sugar has dissolved. Chill in the refrigerator.
Stir the lemon juice and zest into the sugar syrup.
Pour the mixture into a shallow baking tray or container and freeze for 30 minutes. Remove from the freezer and use a fork to break up the ice into fine crystals. Repeat every half hour until the granita is frozen.
To serve, use a fork to run along the frozen granita to create a snow-cone consistency. Serve in small bowls, glasses, or hollowed-out lemons.
