The method relates to the determination of the volatile water, that which volatilizes at the same time as the chlorine. It is applicable to products having a water content greater than 0,0005 % (m/m). It should not be applied to samples stored in bottles subject to corrosion. The principle consists in absorption of the water by passing the gasified sample into tared absorbers containing phosphorus pentoxide or magnesium perchlorate. Elimination of the gaseous chlorine and volatile impurities by flushing with air or dry nitrogen heated to 80 °C. Absorption of the chlorine in a tared bottle containing sodium hydroxide solution. Weighing of the absorbers to determine, by difference from the original masses, the mass of water.