Viruses in drinking water

Viruses in drinking water can cause infectious diseases. In the past, hepatitis A and E were the most-frequently observed drinking-water-borne viral infections, but in recent years several small- and large-scale norovirus epidemics have been described, even in Europe. All virus species spread via drinking water are of fecal origin. They are regularly identified in waste water even after conventional multi-stage water treatment. The approved disinfection methods can cope with these viruses if they are not integrated in larger particles. For this reason particle separation is particularly important in water treatment. Virological tests are not reliable enough to ensure that drinking water is sufficiently virus-free. The examination of 100 mL of water for E coli and coliform bacteria is not adequate proof either. If potentially contaminated raw water is used, consumer safety must be ensured by calculating the performance of water treatment plants on a case-by-case basis. Such a calculation takes into account the virus load of the raw water, the efficiency of the physical and chemical particle elimination steps and the effect of disinfection. Those factors which determine the effectiveness of disinfection, namely concentration and exposure time or UV radiation strength, must be adjusted according to the risk of viral infection, and calculated settings must be adhered to, even if favorable E. coli levels may make them seem excessive.