Microbiological and virological analysis of water from two water filtration plants and their distribution systems

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Abstract
The microbial flora of the water produced by two water filtration plants and their drinking water distribution system were evaluated: the Pont-Viau (PV) and the Repentigny (RE) water filtration plants. Untreated water entering the plants contained 3.6 (PV) and 16.8 most probable number of infectious units (mpniu)/L (RE) enteric viruses and total coliform bacteria counts were 3000000 (PV) and 500000 cfu/L (RE). Treated water leaving the plant was essentially free of all the bacterial indicators measured (total, stressed, and fecal coliforms; Aeromonas hydrophila; Pseudomonas aeruginosa; Clostridium perfringens; enterococci) as well as of human enteric viruses. Heterotrophic plate counts at 20 and 35.degree. C were low in the freshly treated water leaving the plants, but bacterial regrowth was observed in both distribution systems at all sampling sites. Average counts for the heterotrophic plate count (20.degree. C) were between 106 and 107 cfu/L and counts were clearly increased with the distance from the plant. The most numerous bacterial bacterial genera encountered were Bacillus, Flavobacterium, and Pseudomonas (nonaeruginosa).