Water may contain numerous pathogenic organisms and thereby become a means of transmission for many diseases. These includes: Typhoid and paratyphoid fever, Hepatitis A, Cholera, Poliomyelitis, Diarrhoea (caused by Escherichia coli, Salmonellae, Yersinia enterocolitica), Viral gastroenteritis, Bacillary dysentery (caused by various species of Shigella), Campylobacter dysentery, Amoebic dysentery, Giardia (lambliasis), Balantidiasis, Helminthiasis cause by Ascaris and Trichuris. Also the number of faecalEscherichia coli will be considerably reduced when the raw water is subjected to storage. The pathogenic organisms which may be present in water are numerous and identifying these organisms individually in practice (bacteria, protozoa, helminths etc.) is difficult. As their presence is always linked to faecal pollution (except for guinea worm), it is preferable to look for organisms which are “indicators” of this pollution. The common feature of all these routine screening procedures is that the primary analysis is for indicator organisms rather than the pathogens that might cause concern. Indicator organisms are bacteria such as non-specific coliforms, Escherichia coli and Faecal Streptococci such as Enterococcus faecalis that are very commonly found in the human or animal gut and which, if detected, may suggest the presence of sewage. It is therefore reasonable to summarize that if indicator organism levels are low, then pathogen levels will be very much lower or absent. The count of those colonies which develop with a characteristic appearance gives the number of faecal coliforms in the sample of water.
Apart from analyzing for microorganisms by isolating them, one can also analyse for them in groups like; Total Plate count, Total Heterotrophic Bacteria, Hydrocarbon Utilizing Bacteria, Sulphate Reducing Bacteria, Total Heterotrophic Fungi, Hydrocarbon Utilizing Fungi, Faecal Coliform Count and Total Coliform Count.
Total Heterotrophic Bacteria is a count of aerobic-anaerobic bacteria in water. They are used for detection of all bacteria, but cannot be used in feacal contamination. Heterotrophic bacteria are not indicars of pathogenic conditions but some of them like Pseudomonas is opportunists and can cause some infections in skin and lung and the other type like Aeromonas cause gastroenteritis. They are largely responsible for the process of organic matter decomposition. Many pathogenic bacteria are heterotrophs. However, many species of heterotrophic bacteria are also abundant in the environment and are considered normal flora for human skin.
The total coliform count is the total number of coliform bacteria formed in a cultured water sample while the faecal coliform count is the total number of faecal coliform bacteria present in a sample. The coliform bacteria are facultatively anaerobic, Gram-negative, non spore-forming rods that ferment lactose vigorously to acid and gas at 35 2oC within 24 to 48 hours. There are different bacteria that forms the faecal coliform but Escherichia coli is the most preferred faecal coliform used in assaying water analysis because it gives indication of faecal contamination
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