The purpose of this standard is to specify a method that allows plotting the representative curve of the water solubility of an anionic surface agent as a function of temperature and, consequently, evaluating its solubility for a given temperature. The method is applicable to both pure surface agents and technical products or formulations of liquid anionic surface agents, provided that the solutions of these products are optically transparent and not excessively colored. NOTE — The determination of solubility can be carried out without restriction in the range 0 to 90 °C; for temperatures below 0 °C, it is possible to determine if the solution does not freeze. The solubility curve obtained in the case of pure products may eventually allow the determination of the Krafft temperature.