Analysis in the vicinity of an urban rainwater infiltration sys-tem found that biocidal substances and their transformation products can find their way into urban surface water bodies and even into groundwater. The analysis focused on sources related to potential run-off from building facades and green roofs. The resulting insights make it clear that much more attention must be paid to transformation products, in particular, than has been the case to date and that end-of-pipe measures to retain biocides and their transformation products in rainwater run-off are not completely efficient. Therefore, this article presents and recom-mends holistic strategies that avoid the introduction of biocide residues into the aquatic environment.