Stir the water and sugar in a large saucepan over medium heat until the sugar dissolves, about 5 minutes. Cool completely. Pour the sugar syrup over the vodka mixture. Cover and let stand at room temperature overnight. Strain the limoncello through a mesh strainer. Discard the peels. Transfer the limoncello to bottles. Seal the bottles and refrigerate until cold, at least 4 hours and up to 1 month.