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Microbiological Water Quality Standard - Guidelines for bacteriological water quality differs from country to country, generally keeping with those recommended by World Health Organization. Usually coliform counts are used to setup water quality standards.
It should be noted that standards set using coliform counts are arbitrary and they represent a measure of degree of possible human faecal contamination. The number of coliforms permitted in water is dependent on the purpose for which the water is used. The standards for drinking water are more stringent than those for recreational waters

However, because of the above cited reasons this standard is not always attainable in practice. Therefore, the following tolerance limits have been generally accepted for routine samples.
1.E.coli should not be detectable in any sample of 100ml
2. no sample of 100ml should contain more than three coliform organisms.
3.coliform organisms should not be detectable in any two consecutive samples of 100ml from the same or a closely related sampling point.
4.for any given distribution system, coliform organisms should not occur in more than five percent of routine samples, provided that atleast 50 samples have been examined at regular intervals throughout the year.