Comment by kijin

Yup, distillation never produces a pure product. Cask-strength whiskeys contain quite a lot of water, even though nobody is stupid enough to distill at 100C. Even an industrial column still can't go over 96% ABV.

There is always some amount of vapor pressure, even below the boiling point of a substance. Otherwise, neither water nor alcohol would evaporate by themselves at room temperature! The temperature we call the "boiling point" is just the temperature at which the vapor pressure equals the ambient pressure.