Process schemes for production of high-purity distillate are examined. The analysis was based on the postulate that contamination of vapor (distillate, condensate) with nonvolatile contaminants is due to entrainment of drops of boiling liquid by the vapor stream. Expressions were found for calculating the final concentration of contaminants in distillate for different numbers of stills in the process scheme and fraction (of the initial stream) of sampled product. The analysis was performed for arbitrary and optimum distributions of the streams in the process schemes. It was found in particular that the purity of the distillate decreases when the fraction of sampled product increases.