Public and scientific concern has been expressed on the possible hazards of trace amounts of organic compounds with carcinogenic and mutagenic properties, identified in drinking water. For a number of these compounds, the carcinogenicity is well established according to IARC criteria, but the extremely low concentrations (less than 1 microgram/l) indicate a neglectable risk to humans. Some compounds, mainly volatile halogenated alkylated hydrocarbons, may be present at higher concentrations, but for these the weight of evidence for carcinogenicity often is very poor, being demonstrated in mouse liver only. The relevance of mouse liver tumours may be seriously questioned, especially after exposure to hepatotoxic doses and in the absence of sufficient evidence for genotoxicity. It is therefore not justified, to use a non-threshold approach in the toxicological evaluation of these compounds. More or less similar conclusions can be derived for the organic "mutagens" identified in water, that is either their concentration is extremely low or sufficient evidence for genotoxicity is lacking. It is concluded therefore, that, at the present time, drinking water in the Western world can be regarded in general as "chemically safe".