Wash the lemons thoroughly and use a vegetable peeler to remove the zest, avoiding the white pith.

Place the lemon zest in a glass jar and pour the vodka over it. Seal the jar tightly and let it sit in a cool, dark place for at least 7 days, shaking it gently every couple of days.

After the infusion period, combine the water and sugar in a saucepan over medium heat. Stir until the sugar is completely dissolved. Let it cool.

Strain the lemon-infused vodka through a fine strainer into a clean bottle. Add the cooled syrup and mix well. Seal the bottle and refrigerate.

Chill the limoncello in the freezer before serving. Serve in small chilled glasses.