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Bacteriological quality of drinking-watera according to World Health Organisation (WHO) |
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Microbiological examination provides the most sensitive indication of pollution of drinking-water supplies*
| Organisms |
Guideline Value |
All water intended for drinking:
E.coli or thermotolerant coliform bacteria b, c
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Must not be detectable in any 100 ml sample |
Treated water entering the distribution system:
E.coli or thermotolerant coliform bacteria b
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Must not be detectable in any 100 ml sample |
Treated water in the distribution system:
E.coli or thermotolerant coliform bacteria b |
Must not be detectable in any 100 ml sample |
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| a |
Immediate investigative action must be taken, if E. coli are detected. |
| b |
Although E. coli is the more precise indicator of faecal pollution, the count of thermotolerant coliform bacteria is an acceptable alternative. If necessary, proper confirmatory tests must be carried out. Total coliform bacteria are not acceptable indicators of the sanitary quality of water supplies, particularly in tropical areas, where many bacteria of no sanitary significance accur in almost all untreated supplies. |
| c |
It is recognized that the great majority of rural water supplies, especially in developing countries, faecal contamination is widespread. Especially under these conditions, medium-term targets for the progressive imprvement of water supplies should be set. |
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