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
Place the lemon peels in a pitcher.
Pour the vodka over the peels and cover with plastic wrap
Steep the lemon peels in the vodka for 4 days at room temperature
Stir the water and sugar in a large saucepan over medium heat until the sugar dissolves
Cool completely. Pour the sugar syrup over the vodka mixture. Cover and let stand at room temperature for 3-7 days.
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.