Sources of Drinking Water

Sources of Drinking Water

	Sources of Drinking Water Water is the most common and important chemical compound on earth. The availability of drinking water has been the most critical factor for survival throughout the development of all life. As the population increased, the natural supply of water became limited, ophisticated techniques and systems were developed to obtain access to new water reservoirs and to distribute water for irrigating and drinking.
Besides hygienic problems caused by unsanitary wastes, the rapid development of industry, especially the development of the chemical industry, has resulted in an ever-present contamination of all kinds of natural water systems. Surface water Streams, rivers and lakes are the major sources. These waters originate from ground water and rain water (surface run off). Surface run off contributes to turbidity and microorganisms. Ground water Wells and springs originating from infiltrated rain water which flows through the underground are also common sources. A little contamination of the ground water occurs from organic and inorganic soil particles, animal and plant debris, fertilisers, pesticides, microbes, etc. as it flows through the soil layers. Partial removal of microorganisms occurs by the death of cells due to lack of nutrients.
Rain water This is of high quality since the only possible source of contamination is airborne microorganisms that too in very low numbers. Based on quality, water can be of the following types. Potable water Clean, safe water free from disagreeable taste, odour, harmful chemicals, turbidity and microorganisms is called potable water. Polluted water Water with added substances which impart colour, odour and taste is polluted water.
Contaminated water This is water which is unsafe for drinking since it may have added discharges from human or animal intestines, or is rendered dangerous by addition of poisonous chemicals. Water may contain various contaminants and pollutants including faecal contamination, presence of disease causing pathogenic organisms, organic and inorganic colloids, clay, microbial debris, reduced iron and manganese compounds and floating or large suspended solids (leaves or branches). To render water fit for drinking and domestic use, treatment of water is necessary. It is essential that the water used for drinking purpose is periodically examined for microbiological parameters.
	The detection and estimation of pathogenic bacteria is a tedious work as the number of these organisms in water is very low. The commonly associated microorganisms in potable water are Salmonella typhi, Vibrio cholerae, Salmonella paratyphi, other enterococci like faecal streptococci, Streptococcus faecalis, Clostridium perfringes and Bifidobacterium species, Salmonella typhimurium and Shigella dysenteriae. The various methods used in the microbiological examination of potable water include:

Detennination of standard plate count This provides density of aerobic and facultative bacteria which can grow at 37°C in water sample.

Most probable number This method statistically signifies the probable number of coliforms or other ontaminating microorganisms that may be present in water.

Filtration By filtering a known volume of water to be analysed through a membrane filter apparatus which has a provision for filtering the microorganisms on its filter pad (having a pore diameter of 0.45m), one can count the number of microorganisms by plating the filter pad directly on the medium.

Gram staining It gives a direct report about the presence of microorganisms in water but it is not reliable like the previously mentioned methods.

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