Remove the peels from the lemons using a vegetable peeler. Reserve lemons for another use. Place the peels in a two-quart pitcher and pour in the vodka. Cover with plastic wrap and allow to steep for 4 days at room temperature.

Combine water and sugar in a medium saucepan and heat over medium heat until the sugar dissolves. Allow to cool completely. Pour cooled syrup over the lemon peels and vodka and allow to sit at room temperature overnight.

Strain the limoncello through a mesh strainer, discard the peels. Transfer to bottle and refrigerate for at least 4 hours or until cold. Keep limoncello in the freezer if desired.