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The presence of coliforms in distribution system samples is one of the major concerns for utilities. Progress has to be made in the area of coliform analysis to allow utilities to improve their control of distributed water quality. The Direct Viable Count-Fluorescent in situ Hybridization (DVC-FISH) method and an enzymatic CHEMSCAN-based method are two new analytical methods. After evaluation, they proved to be more sensitive, specific and rapid than the standardized culture method, and to be well adapted to monitoring distribution system contamination. The study presented here covers a survey in the suburbs of the Paris, France network. Parameters under study were E.coli counts using the DVC-FISH technique, the CHEMSCAN technique and the standardized culture method. The results demonstrate that the water quality was excellent during the study, with very little non-compliance and no confirmed coliform positive sample in the official sanitary control (over 100 samples/week). In spite of these satisfactory results for compliance, the use of the DVC-FISH technique revealed that E.coli were nevertheless present in the distribution system, although not detectable with agar cultures. When comparing E.coli counts obtained with the DVC-FISH and the CHEMSCAN technique, it appears that the DVC-FISH technique leads to a higher number of positive results than the CHEMSCAN technique. The spatial distribution of positive samples appears to be uneven, with 4 points which were never positive, and 2 which were positive in 47% of cases. The use of this new analytical technique proved to be very promising, and to give an appreciably better insight into water quality. One of the major problems for utilities is the significance of coliform positive samples, and these new techniques obviously are an alternative to current bacteria counts. There is therefore a good potential for application in drinking water monitoring, allowing utilities to anticipate non-compliance and take protective measures in time. Includes 6 references, tables, figures.

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Edition: Vol. - No. Published: 06/01/2001 Number of Pages: 9File Size: 1 file , 290 KB