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

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

In a saucepan, combine the water and sugar. Heat over medium heat, stirring until the sugar is completely dissolved. Allow to cool.

After the infusion period, strain the vodka mixture through a fine mesh strainer to remove the zest. Mix in the cooled simple syrup to taste. Bottle the limoncello and refrigerate.