This opinion paper assesses for the UK, whether the current use of cytotoxic drugs, one of the most toxic pharmaceuticals in common use, could pose a risk to aquatic organisms and to humans through water recycling. A water quality model was set up for one of these drugs, 5-fluorouracil, in the Aire and Calder catchment in Northern UK. The study predicts 5–50ng/L concentrations for long stretches of this catchment under low flow conditions. Due to their mode of action, practically all eukaryotic organisms are vulnerable to damage, with teratogenicity being the greatest concern at such levels. However, it is unclear to what extent the predicted low concentrations would affect flora and fauna in receiving waters but there may be an additive effect of a mixture of cytotoxic drugs which should be taken into account. The exposure of the pregnant mother, or more specifically her foetus, to these drugs via drinking water should be minimised. Current drinking water purification technology gives grounds for optimism on removal of these compounds, but no appropriate data exist yet.