The number of waterborne outbreaks in Finland has decreased in recent years. Over the past decade, there have been an average of two outbreaks per year, compared to around four annually during 2005–2014.
The findings are based on a report conducted as part of the Safe Water for All project, which reviewed waterborne outbreaks from 1998 to 2024. The data included reports from the food and waterborne outbreak registry (RYMY) as well as outbreak records maintained by the Finnish Institute for Health and Welfare (THL).
During the review period, a total of 109 waterborne outbreaks were identified in Finland. Most outbreaks occurred during the summer months, particularly from June to August.
When the causative agent could be identified, the most common pathogens were norovirus and Campylobacter . Most outbreaks were caused by contamination of groundwater. Sources of contamination included wastewater, surface water and runoff . Contamination of water distribution systems also led to outbreaks.
Outbreaks were most frequently associated with groundwater plants and private wells, such as drilled and dug wells. In some cases, contamination was also detected in water distributed through supply networks.
“Although waterborne outbreaks have become less frequent, individual incidents can affect large numbers of people. Therefore, prevention and proper maintenance of water services remain essential,” says Senior Researcher Jenni Ikonen.
The results of the outbreak review will be presented at the Water Services Days in Lahti on 21 May 2026.
Water safety under pressure from multiple directions – preparedness and maintenance are key
Finland’s water services are of a high international standard, but climate change, demographic changes and new security threats are putting pressure on their reliability.
The Safe Water for All project (WaterFall), funded by the Strategic Research Council of Finland, develops methods and tools to strengthen the resilience of water services. The project identifies risks and drivers of change and provides solutions to ensure water quality and availability.
The project consortium includes, in addition to THL, the Finnish Environment Institute, the Universities of Oulu and Lapland, the National Defence University, and Demos Helsinki.
Further information
Meriläinen, P., Laukka, V., Mustajoki, J., Rossi, P., Leviäkangas, P., Halonen, K.-M., Sommarberg, S., Miettinen, I.T. (2026). Safe Water for All – Managing Challenges in Drinking Water Supply. Vesitalous 2/2026.
Päivi Meriläinen
Work Package Lead (Water Quality and Health)
Senior Researcher, THL
Tel. +358 29 524 7826
firstname.lastname@thl.fi
Jenni Ikonen
Senior Researcher, THL
Tel. +358 29 524 6375
firstname.lastname@thl.fi