What is the difference between distilled water and sterile water?

V. BARATHI

Chennai

Distilled water and sterile water are totally different. Water in pristine form, (as in the rain water or water obtained from snow) is called pure water. When water is taken from other sources (that is other than rain water) it may contain salts and other dissolved solids and this is therefore impure water.

To remove these salts or other dissolved solid etc from the impure water the process of distillation is used. Distillation is a process in which water is boiled and heated till it evaporates and the evaporated vapour is cooled, thereby condenses to form water again. This processed water is called distilled water.

Uses of distilled water are for working, cleaning of sensitive chemical plants, machines etc, and in preparation of chemical solutions where pathogens, microorganisms are not of concern. It be noted that distilled water is pure water free from other chemicals etc but is not sterile.

Sterile water is that which inhibits the growth of microorganisms. Since in nature there are a variety of microorganisms which withstand and survive heat treatment even beyond 100{+0}C, these temperature resistant organisms resist and survive after the process of distillation.

Thus the distilled water though pure, is not sterile water. So further processing of distilled water is done to make this water sterile. This is done by autoclaving the distilled water where due to increased pressure in the autoclave (as happens in domestic pressure cooker) the temperature is raised much beyond 100{+0}C due to which the high temperature resistive microorganisms called pyrogens get destroyed, rendering the distilled water sterile.

Thus, the difference between distilled water and sterile water is that whereas distilled water is not free from microorganisms and may permit their growth, sterile water is totally free from microorganisms .No organic growth is possible in this. It is this sterile water which is used for injections and parentaral preparations in pharmacy.

SOM SHANKAR

Assistant Professor of Engineering Chemistry

GITAM University

Visakhapatnam, Andhra Pradesh