Occurrence of Fungi and Actinomycetes in Finnish Drinking Waters

The majority of Finnish drinking waters fulfill all set regulations and consumers consider the quality as good, but microbiological problems do occur. One such phenomenon is taste and odor problems in distributed water. The essential factors in this regard are actinomycetes and microfungi (molds and yeasts) growing in water reservoirs and in biofilms on the surfaces of distribution pipelines. As previous research data about this matter is scanty, National Public Health Institute began in 2004 a research project to elucidate the occurrence of molds and actinomycetes in Finnish drinking water pipeline networks. This research was activated by a nationwide survey which was answered by 450 waterworks. Of these about 10% had odor or taste problems possibly related to the growth of fungi/actinomycetes in their distributed water. On the basis of this survey, 19 ground- and surface- waterworks having microbiological problems were selected for a study of quality changes during the production and distribution of drinking water. Both molds and actinomycetes were found from all the studied waterworks. Yeasts were found only from four waterworks. Still, the concentrations of molds/actinomycetes were low (below 1000 CFU/L). It was found that the quality of raw water explains in many cases the mold problem of the potable water. The occurrence of actinomycetes, meanwhile was mostly connected with microbial regrowth in the distribution network, especially in networks which did not apply disinfection. The diversity of the problem is reflected in that the occurrence of molds/actinomycetes could not be explained besides the disinfection with other factors like pipeline materials, content of nutrients or temperature.