[priyasaravanan_1406]

Water the elixir of life is the basic and important element supporting life on the planet. It is evident in researches carried out to find out the possibility of life forms in other planets stating, the presence of water signifies the presence of life in the explored planet .Thus water is incredible in nature and is an essential element for all lives. Man uses water for drinking, cooking, bathing, washing and other recreational activities and just can’t exist without water. Thus water being a part and parcel of humans and also a natural curative or medicine for good health if contaminated becomes a potential threat to the health, which may even be fatal.

How does water gets polluted /contaminated? There is not one but many ways by which a water body gets polluted or contaminated. Either anthropogenic or non-anthropogenic, the change in temperature, entry of effluents into the water body from any industry, entry of sewage into the water body all accounts for water pollution causing physical, chemical and biological pollution and hence the quality of water is evaluated by analyzing these three categories namely physical, chemical and biological parameters. Physical parameter involves analysis of water for temperature and presence of total suspended solids and turbidity and chemical parameters indicates analysis of water for BOD,COD, heavy metals, pesticides and so on and presence of excess of any of the analyzed chemical in the water than the desired level indicates water contamination. Biological parameter involves the analysis of water for presence of any pathogenic microbes. There are many international standards set to ensure the water quality and any analyzed water sample for various set parameters identified with levels exceeding the set desired levels is said to be polluted or contaminated and attains the status of unfit for consumption.

Water body contaminated with sewage or waste water is most likely to possess pathogenic microbes fatal to humans when consumed and these microbes may be bacteria, virus or protozoa. E. coli, Salmonella, Pseudomonas, Campylobacter and Shigella are some of the bacterial pathogens in water. Enterovirus, Noravirus, rota virus is some of the viral pathogens, Entamoeba, Giardia lamblia are examples of possible parasitic pathogens in the water. There are many water borne pathogenic diseases identified like amoebiasis, giardiasis, cryptosporidiosis, SARS, hepatitis A, botulism, cholera, dysentery, E.coli infection, typhoid etc posing potential health risk and many analytical methods has been derived to detect the presence of such pathogens in the drinking water.

Screening water for the presence of all such pathogens is quite complicated and hence analysis to detect the presence of indicator organism in the water is the most commendable and common method practiced to ensure the water quality based on microbial contamination. Coliforms are the indicator organisms and generally divided as Total coliforms and fecal coliforms. Screening for fecal coliform is significant and presence of this particular strain in analyzed water sample indicates the possibility of presence of harmful pathogens and there are various established methods available to check the water for pathogenic contamination.

The most widely used methods for analysis of water for the presence of the indicator organism (coliforms) are plate count method, membrane filtration method, Multiple tube method or Most probable number (MPN) method. Sterile condition should be ensured right from the sample collection till the end of the analysis procedure. In multiple tube method, 0.1ml, 1ml and 10ml of the sample is inoculated into tubes with selective liquid media (5 tubes per dilution and hence total of 15 tubes) and incubated at required temperature for required time. The presence of coliforms is indicated by the formation of gas in the tubes. The tubes are observed after 24 hours and 48 hours of incubation. The number of tubes positive for gas formation is counted in each set and the most probable number is calculated by comparing the result to the existing derived standard MPN chart. To detect the presence of fecal coliforms, sample from the positive tubes are inoculated into the lactose bile broth and incubated. Presence of fecal coliforms is confirmed by the gas production.

The other method to test the coliforms is the membrane filtration method which is employed to test large volume of sample say 100ml. In this method the sample is passed under vacuum pressure through specially designed membrane and the membrane is transferred to the prepared selective agar plates and incubated at 44.5 degree Celsius for 24 hours. The plate is observed for colony forming units and the number of colonies present in the sample is calculated. Apart from this now a days there is a special method called enzyme-substrate assay available to test the coliforms in the water.

Thus drinking water quality is ensured by analyzing all the three parameters like physical, chemical and biological parameter. Even any one of the parameters not falling under the prescribed standards makes the water unfit for consumption.

[ExpertScie]

There are various methods which are employed in microbial evaluation of water: Few of them are aligned with today’s modern technology and few are based fundamental microbiological concepts.

1)ATP Testing:
In this method, detection of Adenosine Triphosphate or ATP is done and this helps to rapidly measure active microorganism in water. The Principle of this testing is that ATP molecule is found only in and around living cell and therefore such measure will be directly related to the biological concentration. Further this measure is classified depending upon the type of life. The ATP is quantified by measuring the light produced through its reaction with the firefly enzyme Luciferase using Luminometer.

2)Multiple Tube Method :
This method is based on fundamental concept of microbiology. This is one of the oldest methods.
In this method, the measured sub-sample is diluted for example the 10ml sample is diluted with 100 ml sterile growth medium. Further, aliquot of 10ml is decanted into each of the tubes. Such way, the dilution range of 1:10 through to 1:10000 is produced. After incubation, the number of tubes with growth is counted for each dilution. The standard calibration plot or standard table is then referred to know the concentration of organism in the original test sample.

3) Membrane Filtration:
The serially diluted samples are vacuum filtered through membrane filters and these filters are then laid on growth media like nutrient agar. Membranes have a printed millimeter grid on and can be reliably count.

Such methods help in microbiological evaluation of water and can conclude on the type and its suitability.