Many species of microfungi are reported in aquatic ecosystems with different frequency. Their number constantly fluctuates depending on the concentration of environmental and anthropogenic factors. Drinking water, tap and bottled, is essential for the proper functioning of the human body. It is also the main component of food and hence it should be safe for human health and free of contaminants. The mycological purity of tap water in two large cities in the region (Olsztyn and Ostrołęka) and a small village (Gągławki) as well as bottled, medium-mineralized and curative water stored under different conditions were tested. The laboratory investigations followed a pathway applied in diagnostic mycological laboratories. The conducted tests demonstrated that microfungi were found in tap water originating from the cities and in bottled water. The rural water supply system was free from contaminations. Eighteen species of microfungi were identified in tap water from Olsztyn and 9 species in tap water from Ostrołęka. In bottled water, 13 fungal species were detected. Exophiala spinifera and Debaryomyces hansenii were recorded in the water supply systems of both cities, while one common species, i.e. Aspergillus fumigatus, was identified in tap water fromOstrołęka and in bottled water. The conducted studies have significant practical implications, for instance in sanitary and epidemiological water evaluation and in medicine in the context of analysing the quality of drinking water in reference to health resorts and nosocomial infections.