Microbiological Guidelines for Wastewater Reuse
Wastewater contains high concentrations of excreted pathogens such as viruses, bacteria, helminths
eggs, and fecal coliforms. These excreted pathogens have the potential to cause disease if present
in a human host in sufficient quantities. Intestinal nematodes pose the highest degree of risk of
infection while bacteria pose a lower risk. Viruses exhibit the lowest risk. To minimize the potential
risk of infection, the World Bank, World Health Organization and International Reference Centre
for Waste Disposal at Engelberg, Switzerland, convened a group of experts comprising of
epidemiologists, social scientists and sanitary engineers in 1985, to review recent epidemiological
evidence, and make recommendations. This report was the basis for the WHO guidelines on the
safe use of water for agriculture and aquaculture. The rationale behind the WHO guidelines
outlined below, was to develop criteria that would prevent the transmission of communicable
diseases while optimizing resource conservation and recycling.
Restricted irrigation: no more than one viable human intestinal nematode egg per