This International Standard specifies an azeotropic distillation method for the determination of the water content of surface active agents and soaps. Volatile matter soluble in water but insoluble in xylene or Petroleum will be included in the result. The method is applicable to products in the form of powders having water contents greater than 5 % (m/in), and in the form of pastes and solutions. lt is not applicable to samples containing water-soluble volatile compounds, for example ethanol. With regard to soaps, as the results cannot be obtained with an accuracy greater than 0,3 %, this method should be used only for soaps containing appreciable amounts of volatile matter insoluble in water. The use of this method is also recommended for soaps made with linseed oil or other drying oils and for certain soaps containing, for example, sodium silicate. The azeotropic distillation method is applicable only if so indicated in the specific Standard for each product.