Denatonium is one of the bitterest substances known to man and therefore applied in numerous consumer products to prevent an accidental or intentional consumption. So far no information was available on the occurrence of this compound in the environment. A sensitive targeted method was developed and applied to water samples taken in the federal state of Baden-Württemberg, Germany. Denatonium was detected in 100% of the investigated 22 wastewater treatment plant (WWTP) effluents with a maximum concentration of 341 ng L−1. Additionally, water samples were taken from the Ammer river over a period of one week and all wastewater impacted samples showed denatonium at concentrations up to 195 ng L−1. Retrospective analysis of high-resolution mass spectrometric measurements of WWTP effluents from Italy and Switzerland confirmed and therefore point to an international occurrence of denatonium as anthropogenic contaminant.