Zest the lemons using a microplane, avoiding the white pith. Place the 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. Remove from heat and let cool.

After the infusion period, strain the vodka through a fine mesh strainer to remove the lemon zest. Mix the infused vodka with the cooled simple syrup. Adjust sweetness to taste.

Pour the limoncello into clean bottles and seal. Store in the freezer for a refreshing drink.