[The occurrence of salmonellae in drinking water (author's transl)]

A total of 7187 samples of drinking water from different areas of the Lower Saxonian District of Braunschweig was investigated according to regulations of the Trinkwasser-Verordnung during June 1977 and May 1979. The bacteriological results are given in Tab. 1 and 2. Salmonellae were isolated in three samples of drinking water and in one sample of sludge from a municipal pipe of drinking water (see also Tab. 2). Additional experiments confirm that growth of salmonellae and other enterobacteria is possible in that sludge (Fig. 1 and 2). These findings implicate some considerations: E. coli and coliforms are the most important microbial water quality indicators of the Trinkwasser-Verordnung. It is presupposed that, when the indicator density is low (less than 1 per 100 ml) the probability that pathogen are present also will be very low. But the question is how low. The risk factor may be estimated on the base of the E. coli-Salmonella ratio in raw sewage of about 10(6). But this relation lessens already in effluents of sewage treatment plants to 10(3) and it seems to be often 10(2) in inadequately disinfected drinking water. For example, we have found four Salmonella serotypes and 408 E. coli during two years. Therefore, the judgement of the presence of E. coli or coliforms in samples of drinking water must impact highly on the improvement of the water quality by disinfection in future.