Zest the lemons, and place zest into a large glass bottle or jar. Carefully zest the lemons with a zester or vegetable peeler so there is no white pith on the peel. Pour in vodka. Cover loosely and let infuse for 10 days or up to 30 days.
In a large saucepan, combine the sugar and water; bring to a gentle boil and let boil, approximately 5 to 7 minutes. Remove from heat and let the syrup cool before adding it to the Limoncello mixture.
Discard the lemon zest and strained Limoncello in a coffee filter.
