Recently, considerable interest has developed regarding the presence of pharmaceuticals in the environment, but there has been comparatively little study on the potential of these substances to enter potable supplies. This is surprising because drinking water would provide a direct route into the body for any drugs that might be present. Although many countries employ advanced treatments, such as granular activated carbon, membrane technologies, ozonation and ultraviolet radiation, for treating water intended for human consumption, some compounds have been shown to be unaffected by such processes. Here, we examine the levels of drug substances reported in drinking water around the world. The possible implications of the presence of these compounds are highlighted and assessed, and recommendations are made for further research.