5 Hygienic considerations Predominantly with domestic sewage the issue of contamination with bacteria or viruses is extremely important. However, also with industrial wastewater pathogens might occur and should at least once in the beginning be analyzed. Usually the coliform bacteria is taken as an indicator organism. In 1985 World Bank, UNEP, UNDP and WHO released a study giving recommendations for irrigation water used for raw consumable crops: Coliform bacteria ≤ 1000/100 ml; Helminths eggs: ≤ 1 (Note: European rivers, for example, have a count of coliform bacteria around 100/100 ml). UNEP (1997) consider the protection of public health, especially that of workers and consumers for one of the most critical steps in any reuse program. To this end, it is most important to neutralize or eliminate any infectious agents or pathogenic organisms that may be present in the wastewater. For some reuse applications, such as irrigation of non-food crop plants, secondary treatment may be acceptable. For other applications, further disinfection, by such methods as chlorination or ozonation, may be necessary. Table 6 presents a range of typical survival times for potential pathogens in water and other media.