Drugs and medicines are characterised by their powerful effects and wide-ranging benefits in certain areas of application. However despite their beneficial therapeutic effects, some drugs affect organisms in the environment and ecosystems, and from the point of view of environmental hygiene, contamination of groundwater and drinking water is highly undesirable, even if the compounds involved have a low acute toxicity for humans. It is not clear whether the dynamics of bacterial population in the environment are influenced by the input of antibacterials and resistant bacteria. Our current knowledge shows that harmful effects for humans are not to be expected from the intake of pharmaceuticals with drinking water. As far as humans and organisms in the environment are concerned, the extent to which a comparison of a short-lived high dose (for diagnosis and treatment) and a long-term low dose (intake via drinking water) is permissible, is open to question, not least because of the polymorphic differences in sensitivity and the responsiveness of individual persons.