Bacteriology
 

Bacteria within water supplies are broadly classified into two groups: the autoclthorous group  (Greek- autocthon, "one sprung from the land itself"), which belong at that location, and the allocthonous group (Greek- allos, "other"), which arrived via contamination, of runoff and rainfall and typically have a limited life span.  Bacteria that are of concern from the public health standpoint fall into this latter group.  Often their normal locale is warm-blooded animal intestines and their presence in water is indicative of sewage or fecal contamination.  Bacteria that are significant interest to public health include salmonella, shigella, leptospira, pasturella, vibrio, E. coli, Yersinia, and mycobacterium.