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Chapter 8*: SANITARY INSPECTION AND MICROBIOLOGICAL WATER QUALITY - page 37 / 52

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Figure 8.4 Counts of faecal coliform bacteria per 100 ml at bathing areas A and B (see Table 8.8) displayed as control charts, with warning and action limits at two and three logarithmic standard deviations respectively above geometric mean counts

The results and recommendations should be discussed with any interested parties before the report is released formally. A contingency plan should also be developed, with the assistance of any interested parties, to investigate and respond to cases of illness or to any unforeseen event or condition that could lead to a deterioration in water quality and possibly increase the risk of illness or danger to bathers. Consideration should also be given to preparing a nontechnical report for the general public.

8.8 Quality control

All laboratories should guarantee that the results of the microbiological analysis of a water sample actually originated from the sample and were not introduced accidentally during sampling or analysis. To support this guarantee, internal and external quality controls should be implemented (Tillett and Lightfoot, 1995). Quality control is described in detail in Chapter 4. Internal quality control includes constant monitoring of equipment (pH meters, balances, pipettes, sterilising equipment, incubators, etc.) and reagents (membrane filters, culture media, buffer solutions, etc.) using controls and reference materials (PHLS, 1994; APHA/AWWA/WPCF, 1995; Janning et al., 1995). Working practice should also be included in this quality control, as well as the precision of the techniques (MPN and MF techniques). In addition, controls have to be made at regular intervals (PHLS, 1994; WHO/UNEP, 1994c). External quality controls are meant to establish good performance by comparing laboratory results with those of other laboratories testing the same artificially prepared sample (Tillet et al., 1993; PHLS, 1994).

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