Zest lemons, making sure not to include any pith. Put zest in a jar with alcohol and let stand in the dark for 3 days, making sure to shake the jar at least twice a day.
When the lemons are pale, all the oil has been extracted. Strain the liquid and discard the zest. In a saucepan over low heat, heat water and sugar until sugar dissolves and syrup is clear. Let cool to room temperature and mix with infused alcohol. Strain liquid through a coffee filter.