ABSTRACT
More stringent control of water contaminants and higher quality standards apply to water intended for human consumption than for other uses. Standards are expressed in terms of the microbiological, the chemical and the physical characteristics of the water. The microbiological quality of drinking waters is typically expressed in terms of the concentration and frequency of occurrence of particular species of bacteria. Chemical and physical water quality standards are commonly laid down for treated waters. These embrace both pollutants which constitute a health hazard and qualities of the water which may give it an unpleasant taste, odour, appearance likely to discourage its use. Sewage with an industrial component may contain heavy metals, toxic organic compounds and other substances toxic to people and other living things. Water quality for recreational or religious bathing is not often identified as a serious health problem in low income countries.
