Combine the water and sugar in a pot and heat while stirring until the sugar dissolves. Remove from the heat and let cool.
Use a vegetable peeler or small knife to remove the peel from the lemons. Be careful you don’t cut too deep, you don’t want any of the white pith. Place the peels in a whipping siphon and add the vodka. Seal the siphon and charge fully. Gently swirl the siphon and let sit for 5 minutes. Place a towel over the nozzle and vent the whipping siphon.
Pour the vodka and lemon peels into the sugar water, cover, and let sit overnight at room temperature. The next day, strain the limoncello. It is now ready to use or can be stored in the refrigerator for several weeks.