The present text is the first part of a paper aimed at specification of the requirements ensuring effective disinfection of drinking water. The discussed health hazards result not only from the presence of pathogenic microorganisms in water, but also from the occurrence of micro- and macroscopic plant and animal organisms. It was shown that while the traditional method for water treatment and disinfection reduces the number of these organisms, it fails to eliminate them completely, particularly in the case of tap water intake from shore intakes of surface waters.