The author explains the importance and types of epidemiological studies used in investigations of the carcinogenic potency of some contaminants or naturally occurring constituents of drinking water. He refers to the work of the American epidemiologist Kenneth P. Cantor who in 1996 evaluated critically more than 200 studies concerned with the above subject as well as more recent studies published in 1997-1999, to make the readers familiar with conclusions for which substances in drinking water there is evidence of an increased carcinogenic risk and where this is not the case. The evaluation pertains to the following substances: disinfec- tion by-products, nitrates, arsenic, cadmium, nickel,asbestos, radionuclides, fluo- rides, hardness of water (Ca+Mg), volatile organic substances and some other industrial chemicals. In the conclusion a historical review is presented on at- tempts of epidemiological studies on the subject of „drinking water and cancer“ in the Czech Republic.

        Key words: drinking water - neoplastic diseases - epidemiological studies