CHAPTER ONE

1.0                                                       INTRODUCTION
Water is the one of the most common substances known and it is good solvent for many substances, water occur at room temperature as clear, colourless, tasteless liquid which freezing into ice at zero degree centigrade and boil at 1000c. it is essential for life on earth. 
According to World Health Organization (WHO) in 1967 is the most important need of living things, it is second only to the air we breath, in fact some scientist believe that all life began in water. Also water is a molecule that consist of two hydrogen atoms and one oxygen atom, when these atoms are heated to a high temperature they join to for water. It occurs in three natural states solid, liquid and gaseous states. Water and ice covered about 75% of the earth surface and water vapour is an important constituent of the atmosphere (Ababio 1985) It exists under major two types which include:. 
Surface Water: They include the streams, lakes, and shallow wells. The air through which the rain passes may contaminate the water.

Ground Water: They originate from deep well and subterraneous springs. This is virtually free of bacteria due to filtering action of soil deep sand and rock. However, it may be come contaminated when it flows along the channels. 
Water in Microbiology can be contaminated when it contains a chemical or biological poison or an infectious agent. These condition also apply to water which is polluted except that the agent or poison is often obvious and water carries an unpleasant taste or appearance. (Encyclopedia America 1988). 
Portability refers to the drinkability of water when it is fit for drinking, when unportable it is unfit for consumption due to some contaminant or pollutant (Earnet 1974) other sources of contamination are various types of establishments and agricultural farm etc. Possible sources of microbial contamination of a body of water are soil and agricultural run-off, farm animals, industrial waste, discharges from sewage treatment plants and storm water run-off from urban areas.  
Contamination by sewage or human excrement and pollution by animals causes the greatest danger associated with drinking water in most developing countries. So it is necessary to examine the quality of water before consumption.    
Monitoring and detection of indicator and disease causing microorganisms are a major part of sanitary microbiology. Bacteria from the intestinal tract generally do not survive in the aquatic environment. They are under physiological stress and gradually lose their ability to form colonies on differential and selective media (Prescott 7th Edition).