Water
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Water for human consumption must be free from chemical substances and pathogenic microorganisms. Drinking water should not only be safe but also pleasant to drinking is that clear, colorless and devoid of disagreeable test or smell.
Drinking water is liable to be contaminated with sewage or other excreted material which may cause intestinal or other systemic infections. The hazards of water pollution are classified into two broad groups is that biological and chemical.
Biological hazards are due to infected agents which may lead to water borne diseases.
chemical pollutants include poisonous chemical substances, industrial or agricultural wastes.
Faecal pollution of water supplies may lead to various water borne diseases. the object of microbiological study of water supplies is to detect whether pollution of the water by Pathogenic organisms has occurred or not. Though it would be ideal to demonstrate the possible pathogens in the water, but it is not practicable as they are usually few and far out number by non pathogenic organisms. Hence we raly on tests that detect indicators of human animal faecal solutions i.e. intestinal organisms. The organisms most commonly used as indicator of pollution are E.choli and the coliform group. In certain conditions Streptococcus faecalis and clostridium perfringens are also searched for.
Bacterial flora in water
The bacteria found in water can be divided into three groups -
Natural water bacteria
The organisms that are commonly found in water free from gross pollution are included in this group.
Soil bacteria
These organisms are frequently washed into the water during heavy rains. these are not normal inhabitants of water.
Sewage bacteria
Many of the organisms included in this group are normal inhabitants of the intestine of man and animals other live mainly on decomposing organic matter.
Factors determining the number of bacteria in water -
Type of water - surface water is more likely to be contaminated, deep waters are generally pure.
Temperature - when organic matter content is high, rise in temperature leads to multiplication of bacteria. Low temperature favours the survival of bacteria.
Organic matter - when organic matter is plentiful, organisms are abundant.
Light - sun rays can be bactericidal provided the water is clear and static. these can penetrate only to a depth of 5 feet.
Acidity - acidity of water has a bactericidal action and plays a considerable part in the purification of some water.
Salinity - A high salinity has a deleterious effect on most bacteria however halophilic bacteria can survive in saline water.
Protozoal content - Protozoa by ingesting and destroying bacteria play a part in bringing down the bacterial number.
Storage - storage of water decreases bacterial count due to sedimentation and devitalisation.
Bacteriological examination
collection of water samples - water samples are to be collected in heat sterilized glass bottles of 230 ml with ground glass stoppers protected by craft paper. To neutralize the bactericidal effect of chlorine in water a crystal of sodium thiosulfate is introduced into the bottle prior to sterilization.
1. sampling from a tape or pump outlet - clean the tape or pump outlet from outside a tape is turned at maximum flow rate and let the water flow for 5 minutes open the stopper feel the bottle and replaced the stopper.
2. sampling of water from a Reservoir (streams, rivers, lakes and tanks) - the stopper is removed and bottle is submerged to a depth of about 20 cm with mouth facing award if there is a current the bottle should face the water current.
3. sampling from a dug well.
Transport
Water bottles should be wrapped in a craft paper the water samples should be properly labelled with details of the source time and date of collection. these should be delivered to the laboratory as quickly as possible where delay is anticipated the bottle should be kept on eyes preferably in an ice box and protected from light.
Methods of analysis -
The standard test usually employed for water bacteriology are:
Presumptive coliform count
Differential coliform count
Detection of physical Streptococcus and clostridium perfringens
Membrane filtration test
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