Risk assessment of parasites in drinking water
Report no: 2009: 28
The Norwegian Scientific Committee for Food Safety (VKM) has carried out a risk assessment of the parasites Giardia and Cryptosporidium in drinking water. The risk assessment concludes that most consumers in Norway are not exposed to parasites in drinking water on a daily basis under normal conditions.
Water treatment that reduces the level of parasites by at least 99% gives a good protection against exposure.
Based on two incidents, the Norwegian Food Safety Authority (Mattilsynet) asked VKM to undertake a risk assessment concerning a health risk from the parasites in the drinking water, with special focus on the parasites Giardia and Cryptosporidium.
Giardia duodenalis and Cryptosporidium of various species, may result in community-wide outbreaks of disease (giardiasis and cryptosporidiosis) if they contaminate water supplies and are not removed or inactivated by the water treatments in place.
Data on the occurrence of these parasites in the animal populations of Norway is more extensive, although incomplete, and indicates that both parasites are widespread in both domestic and wild animals, with species/genotypes of zoonotic potential occurring relatively widely.
Data on the occurrence of these parasites in water supplies before water treatment conducted in the 1990s, indicates a general widespread low level of contamination, as has been reported from many other countries.
Outbreak situations are more likely to occur when a combination of events results in contamination increasing above this level, along with failures in treatment.
The VKM Scientific Panel on biological hazards has been responsible for this risk assessment.