All living organisms need water to maintain their vital functions, while access to clean water is a human right. In human communities, clean water is important also for recreational use. However, the availability of clean water is not a given. Rather, it requires continual anticipation even in Finland and other countries with an advanced water supply and well-functioning sanitation. Research-based knowledge and effective measures for water quality assurance are key to ensuring water security. In our research projects, we are investigating the pollutant sources associated with water resources and developing special analytics needed to establish the chain of events related to water pollution incidents.