This work examines the variation in removal efficiency of triclosan in wastewater treatment works in the United Kingdom between November 2003 and April 2004. Concentrations of triclosan were measured at set points within three different types of wastewater treatment works: rotating biological contactors, trickling filters, and activated sludge. Overall removal of triclosan through these plants ranged from 58 to 96% (rotating biological contactors), 86 to 97% (trickling filter), and 95 to 98% (activated sludge).