220 Microbes and You 



water for his personal drinking, bathing, and cooking needs, but 

 industries which grow up with a community draw heavily on water 

 supplies. To provide the benefits of these services, the one- 

 hundred-gallon figure is useful in the calculation. 



DEFINITIONS 



Whenever sudden, widespread disease breaks out, the water 

 supply is one of the first suspicions by the public. With the 

 careful attention devoted to providing a clean, safe, public water 

 supply, such fears are usually unfounded. This has not always 

 been so, however, and many serious epidemics have been traced 

 directly to polluted water. But before pursuing this topic further, 

 a few definitions of accepted terms seems warranted. 



1. Pure Water. To a chemist, pure water means a liquid with 

 a combination of two parts of hydrogen and one part of oxygen, 

 but to a microbiologist it is understood to be water which contains 

 no disease-producing bacteria or chemicals harmful to man or 

 animals. Safe water is understood to be pure water, since a 

 laboratory examination confirms its potability. 



2. Impure Water. This is considered to be the reverse of our 

 definition for pure water. Impure water contains bacteria or 

 chemicals known to be harmful to man or animals. 



3. Polluted Water. People formerly called this contaminated 

 water, and it indicates that sewage has found its way into the 

 supply. Since human or animal wastes may contain pathogenic 

 organisms, polluted water is potentially dangerous. 



4. Dangerous Water. When one wishes to specify that water 

 contains known disease-producing microbes, it is necessary to be 

 more specific than merely to say that the water is polluted or 

 contaminated. Polluted water contains sewage which may or 

 may not cause disease, and contaminated water may have a high 

 bacterial count due to saprophytic organisms. The term "infected" 

 water is sometimes used, but this is probably a misuse of the word. 

 Tissues may become infected but water, strictly speaking, may not. 

 Perhaps "dangerous" is a better designation for water that is po- 

 tentially harmful because it contains known pathogenic organisms. 



