Detection of viruses in raw water as a basic tool for risk assessment

Human pathogenic viruses may end up in surface waters by fecal contamination. However, the German drinking water ordinance requests that pathogens in drinking water should not be present in concentrations constituting a potential danger to human health. Since many viruses do have a very low dose of infection, they have to be sufficiently eliminated in the process of drinking water purification. Waterborne virus outbreaks in Europe, over the last few decades, were mostly linked to noncompliance with the generally accepted codes of practice for drinking water production. The aimed level of protection of drinking water supplies in Germany, however, exceeds prevention of outbreaks by even protecting against sporadic virus infections. Documentation of such a high level of protection is not achieved by end product control alone but requires a process analysis with risk assessment. To do such an analysis, information regarding the presence of viruses in the raw water used for drinking water production, as well as data of virus elimination rates during purification processes, are of major importance. This paper presents suggestions for implementation of such a risk assessment, focusing on the evaluation of raw water quality.