ABSTRACT
Swedish water purifi cation plants are constructed to take care of bacteria. Chlorine is used as the preferred disinfectant in both surface and groundwater purifi cation plants. However with climate change and increases in the events of heavy rain, the risk increases of contamination of water sources with human, animal and soil pathogens, mainly bacteria, viruses, and protozoa (The Commission on Climate and Vulnerability 2007). The chlorine doses that are currently used in Sweden are not suffi cient to deal with viruses and are ineffective for protozoan control. A major water-borne outbreak occurred in the city of Östersund in northcentral Sweden in 2010. Thousands of people were infected with the protozoa Cryptosporidium. The cause of the contamination was detected to be sewage that by mistake had leaked into the municipality’s main water source i.e. Lake Storsjön, according to the epidemic intelligence work done by The Swedish Centre for Disease Prevention and Control, SMI. It took nearly three months before the tap water was considered safe again. During this time period people were instructed to boil all water that was to be used for food preparation, drinking, and teeth-brushing. An UVfi lter had to be installed in the water purifi cation plant.
