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Payment, P. (1995) Health Significance of Bacterial Regrowth in Drinking Water: Free Opinion. Rev. Sci. Eau 8 (3) : 301-314. [bilingual]

Simultaneously published in french under the title: Effets sur la santé de la recroissance bactérienne dans les eaux de consommation: Tribune libre.

Communication presented at the International Symposium Matière Organique Biodégradable, École Polytechnique de Montréal, June 1994

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The presence of heterotrophic bacteria in drinking water (tap, point-of use treated or bottled) poses a difficult problem because we do not clearly know if they are really innocuous. Two points of views are presented: they could be totally unimportant whatever their number or they can be opportunistic pathogens and even frank pathogens if they are allowed to multiply in large numbers. These bacteria are not of faecal origin and are not indicators of faecal pollution even if occasionally some can be described as coliforms. Studies in the United States on families drinking water from domestic filtration units did not observe any significant health effects while other researchers have observed an inhibitory effect of these heterotrophic bacteria on coliforms and some pathogenic bacteria. On the other band, recent Canadian studies have observed that high bacterial counts in the water produced by reverse-osmosis units were correlated to gastrointestinal illnesses and that bacteria of potential virulence were present in tap water. All these observations have brought back the question of the potential health effects of heterotrophic bacteria. At the same time, the ability of current water quality indicators to protect public health is questioned and we must find other methods for the surveillance of waterborne diseases. Within these new guidelines or regulations, will probably have to set a limit on the acceptable number of heterotrophic bacteria in water. What this level will be remains to be determined, but until then we must assume that it is prudent to test drinking water in such a way, that it will not promote or permit the uncontrolled multiplication of bacteria of which we know so little. We are discovering new pathogens each year and we cannot assume that they are not present in treated waters. There are two approaches that can be used to limit potential health risks. The first is to limit the total population of heterotrophic bacteria by limiting available nutrients and using appropriate enumeration methods (heterotrophic plate count or epifluorescence viable counts). The second is to use or develop an indicator of health risk based on the virulence of bacteria (i.e., detection of virulence factors). There are still long discussions and researches ahead, but the driving force will be probably directed at limiting the nutrient available to heterotrophic bacteria and preventing significant growth in water distribution systems.

Corresponding author

P. Payment, Institut Armand Frappier, Université du Quebec, 531 Boul. des Prairies, Laval (Québec), H7N 4Z3 CANADA

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