MICROBIOLOGY OF WATER
The drinking water of most communities and municipalities is obtained from surface sources – rivers, streams and lakes.  Such natural water supplies are likely to be polluted with domestic and industrial water.  Many city dwellers (whose water comes from the rivers) are not  aware that a considerable portion of their drinking water  may have  been  used  earlier  for  domestic  and  industrial purposes.   Water is used for bathing, washing clothes, washing utensils and flushing toilets.  The domestic water consumption may vary with the availability of water.  Most of the water taken into the  houses may be returned as waste water through drainage system.  All these waste waters contain organic and inorganic waste as suspended or dissolved matter.  In addition, these waste waters contain microorganisms, including those of faecal origin and pathogenic nature.  As a potential of pathogenic organisms, water can be in danger to health  and  life.   The  pathogens most  frequently transmitted  through  water  are  those  which  cause infections  of  the intestinal  tract,  namely,  typhoid  and  paraty phoid bacteria, dysentery (Bacillary) and cholera bacteria and  viruses.  The causative organisms of these diseases are present in the feces or urine of an infected person.

Distribution of microorganisms in aquatic environment
Microorganisms occur in all depths.  The surface film and bottom sediments have a high concentration of microorganisms.  Drifting microbial life of aquatic environment is called  Plankton. It is composed of Phytoplankton  eg. Algae and Zooplankton.  The bottom region of the body of water harbours largest number and kinds of microorganisms called benthic microorganisms.

The movement of water by wind, tide and currents affect the distribution of microorganisms  up welling occurs in oceans.  It is a process in which the bottom water carries with it a rich supply of nutrients and delivers it to the surface region.

Aquatic microorganisms in ponds and lakes
The zonation and stratification of lakes and ponds influence the occurrence of microorganisms. Lakes and ponds of temperate region show thermal stratification, which influences the microbial population in different seasons.  In spring and autumn mixing occurs resulting in massive growth of algae called bloom.  Lakes and ponds enriched with nutrients show eutrophication. The common microorganisms found in fresh water are  Pseudomonas, Flavobacterium,  Aeromonas  and Alcaligenes.  Estuary is semi-enclosed coastal water body having connection  with the open sea.  It receives fresh water with all particulate suspensions through rivers.  In areas receiving domestic wastes with organic nutrients contain the following organisms: Coliforms, Faecal Streptococci, Bacillus, Clostridium, Thiothrix  and  Thiobacillus.  Soil bacteria such as  Azotobacter, Nitrosomonas  and Nitrobacter  are also found  in  water.    Very  few  fungal  organisms  from  the  classes Ascomycetes  Phycomycetes and Fungi-imperfecti are also present in water.

Aquatic microorganisms in the sea
The sea is the largest natural environment inhabited by microbes. Bacteria, algae, protozoa, molds and yeast are major groups of microorganisms found in the sea.  The number of microorganisms is more in coastal waters and it gradually decreases in the open sea. In sea, phytoplanktons form group of microorganisms which convert radiant energy into chemical energy and which support the entire population of fishes eg. 

Importance of aquatic microbes
Aquatic microorganisms, both plants and animals, interact among themselves and between microorganisms. Algae, protozoa and other phytoplankton play key role in the food chain in water and certain organisms perform photosynthesis.  They are called primary procedures in an aquatic ecosystem.  Bacteria and other fungal organisms also play an important role in biogeo chemical transformation in soil.

Sources of water pollution The only source of potable fresh water nature provides is the rain water.   This itself gets polluted by the action of nature, as water falls on land and runs as stream, gathering different types of minerals and suspended particles.  In this running water, due to anthropogenic activities, more minerals, more chemicals and organic materials are added, that makes the water polluted.  There are three main sources of pollution of waters.

1.   Sewage or Municipal effluents : The quality of water after bath, kitchen work, washing of clothes and animals etc.  a large volume of raw  sewage discharged into the main stream pollute the river waters.  Among the various sources of water pollution, sewage, the domestic waste containing decomposing organic matter is the major source and it accounts for 70 per cent of water pollution.  Industrial effluents account for 15 percent of water pollution

2.  Industrial effluents :  The industrial effluents are classified under the following heads.

Potable and contaminated water Water free from disease causing organisms and free from harmful chemicals is known as  Potable water.  Water contaminated with sewage, domestic or industrial waste with chemicals and pathogenic microorganisms is termed as  contaminated water  or polluted water.

Standards for waterThe characteristics of water from various sources depend onrain, nature of substratum on which it is in contact and the effect ofother substances added to it.  The chemical analysis of water is neces-sary to ascertain the quality of water.  For human consumption, potablewater should be used.  Any water can be called as potable water, it if isfree from undesirable odour, flavour and contains no bacteria capableof producing diseases in man.

Indicator organisms : It is almost impossible to isolate from water the organisms re-sponsible for water-borne diseases.  Few organisms are present andthey do not multiply in water.  The only safe method to prevent water-borne disease is to condemn fecally polluted water as being unfit forhuman use, as it may contain harmful organisms.  Fecal pollution can bedetermined by examination of water for colon bacilli   (E.coli). E.coliis abundant in feces and not found outside intestinal tract in nature.  TheE.coli in water indicates the presence of pathogenic microorganisms inwater, which may be responsible for a number of water-borne dis-eases.  Hence, E.coli is known as indicator organism. Water also con-tains bacteria that resemble E.coli but may or may not be of fecalorigin.  These bacteria also ferment lactose with formation of gas likeE.coli. The other indicator organisms are Streptococcus faecalis Strep-tococcus faecium, Streptococcus bovis, Streptococcus equinus etc.,and Clostridium perfringenes