This document specifies a method for the determination of certain cyclic volatile methylsiloxanes (cVMS) in environmental water samples with low density polyethylene (LDPE) as a preservative and subsequent liquid-liquid extraction with hexane containing 13C-labeled cVMS as internal standards. The extract is then analysed by gas chromatography-mass spectrometry (GC-MS). NOTE Using the 13C-labeled, chemically identical substances as internal standards with the same properties as the corresponding analytes, minimizes possible substance-specific discrimination in calibrations. Since these substances are least soluble in water, they are introduced via the extraction solvent hexane into the system. This document is applicable to the measurement of the following cVMS in rivers, streams, and waste water (influent and effluent): This method can be used to determine cVMS from 0,1 ¼g/l to 250 ¼g/l. In well controlled laboratory environments, where contamination is minimized, the lower end of the application range can be diminished by a factor of up to 10.