Standard Bacteriological Test of Drinking Water

Commonly used standard parameter in bacteriological testing of water is to detect and enumerate the indicator organism i.e. the coliform group of bacteria which is a common group of gram negative bacteria. The principal species in this group are Escherichia coli and enterobacter. "Total Coliform" level is the criterion of sanitary quality of water for a number of reasons. First, many are native to the intestinal tracts of warm-blooded animals and man and enter water with faecal discharge. While relatively harmless, themselves, coliform organisms are found in the company of such enteric pathogens as those responsible for typhoid fever, cholera, and dysentery. Coliform is a useful indicator because they normally survive longer than their disease producing fellow travelers. Thus, once they have died off, the danger is normally past. Faecal Coliforms are positive indication of presence of harmful bacteria. It has become the custom to report the results of the coliform test as a Most Probable Number (MPN) index which denotes the number of coliform bacteria in water sample. To test bacteriological quality of drinking water needs a well equipped laboratory and services of expert microbiologist. Standard Coliforrn or faecal coliform test takes longtime and also expensive.
Water Quality Standards
World Health Organization (WHO), guidelines for drinking water quality states that E.Coli or thermo tolerant coliform bacteria must not be detectable in 100 ml sample of drinking water.