Zest the lemons, being careful not to include any of the white pith with the zest.
Put the lemon zest in a pitcher or jar and add the vodka, making sure the zest is covered.
Cover the container with a lid or plastic wrap.
Store the vodka in a cool, dark place such as a closet or basement for 2 to 4 weeks.
After the vodka has steeped for the extended period, bring the water and sugar to a simmer in a large pot over medium-low heat, stirring until the sugar dissolves.
Allow the sugar water to cool completely.
Strain the vodka into the sugar water, discarding the zest.
Stir the limoncello, then pour it into bottles or jars.