This space-time study of bacteriological response compared the presence of pathogens with indicators contained in surface and groundwater in mountainous regions. A systematic search for bacteria such as Listeria, Salmonella, Campylobacter and Yersinia carried out simultaneously with a search for indicators has shown that these waters can occasionally contain potentially pathogens, though these are generally to be found in small quantities. The most common pathogens found are Campyobacter and Listeria. Salmonella has never been isolated. The presence of pathogens is usually accompanied by the presence of classic indicators of contamination such as Escherichia coli, enterococci and other aerobic bacteria. Exceptions are only to be observed in cases of samples presenting very low numbers of pathogens. Such low pathogen levels have a minimal impact on human health; but we cannot exclude that, during periods affected by specific conditions, higher levels might temporarily occur. Our research has demonstrated that classic indicators can be considered as efficient detectors of pathogens in most cases. When these indicators are used systematically and regularly, the human health hazard can be qualified as low but not negligible. The presence of pathogens, together with their survival capacity, brings the protection measures currently applied to safeguard drinking waters sharply into question.