Using a vegetable peeler, remove the peel from the lemons in long strips (reserve the lemons for another use). Using a small sharp knife, trim away the white pith from the lemon peels; discard the pith. Place the lemon peels in a 2-quart pitcher. Pour the alcohol over the peels and cover with plastic wrap or top. Steep the lemon peels in the alcohol for 15 days at room temperature.

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 alcohol 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