For these reasons, early water-bacteriologists developed the concept of using bacterial
indicators for faecal pollution (Ng et al., 1993). These bacterial indicators are assumed to be an indirect measure of the probability of the presence of pathogens in water but have failed to correlate with protozoan parasites such as Cryptosporidium (Bonadonna
et al., 2002) and enteric viruses (Havelaar et al., 1993).