Transfer of bacteria through water vapor generated at moderate temperatures (30-50 degrees C) in passive solar stills, has scarcely been reported. The objective of this research was to investigate whether bacteria in highly humid atmospheres can get transferred through water vapor in the absence of other transfer media to find their way to the distillate. To achieve this objective, passive solar reactors were chosen as the medium for experimentation, and distillation experiments were conducted by spiking a pure bacterial culture (Escherichia coli, Klebsiella pneumonia or Enterococcus faecalis) in low mineralized water vs. highly mineralized water in the dark under moderate temperatures ranges (30-35 degrees C, 40-45 degrees C and 50-55 degrees C). Results showed that bacteria indeed get transferred with the vapor in stills when not exposed to solar U.V. radiation. The trends observed were adequately explained by a zero-modified Hurdle-Poisson model. The numbers of cultivable bacterial colonies transferred were bacterial size, water type and temperature dependent with highest transfers occurring in E. faecalis > E. coli > K. pneumonia at the 40 degrees C range in low mineralized water. Proper management strategies are recommended to achieve complete disinfection in solar stills. (C) 2014 Elsevier B.V. All rights reserved.