This International Standard specifies a method of determining the water content of rocks. This International Standard is applicable to the laboratory determination of the water content of a rock test specimen by oven-drying within the scope of geotechnical investigations. The oven-drying method is the definitive procedure used in usual laboratory practice. The practical procedure for determining the water content of a rock is to determine the mass loss on drying the test specimen to a constant mass in a drying oven controlled at a given temperature. The mass loss is assumed to be due to free water and is referenced to the remaining dry mass of the test specimen. NOTE This document fulfils the requirements of the determination of water content of rock for geotechnical investigation and testing in accordance with PrEN 1997-2 (2023).