[Qualitative and quantitative determination of bacterial populations in aquatic habitats. 6. Germ regrowth and drinking water].

Regrowth of bacteria in the sphere of drinking water is dependent on time (stagnation of the water in the distribution system) and on the absence or inefficiency of disinfectants e.g. chlorine and chlorinedioxid. Traceable amounts of assimilable organic carbon are not a presupposition for the multiplication of the bacteria. Even in bidistilled water growth of bacteria could be observed. Under laboratory conditions it was shown that the number of bacteria increased to 10(4) per ml after a 4-days-incubation at 20 degrees C. In particular the multiplication is concerned with the autochton bacterial flora of the water e.g. pseudomonas species. As a result of the identification of the bacteria it was observed that the increase number of bacteria was accompanied by a decrease of individual species. After 6-days'-incubation of the water samples pseudomonas-species like P. fluorescens and P. cepacia were the predominating bacterial forms. The number of Gram-positive bacteria decreased significantly during incubation.