A method for measuring the water concentration in a light-diffusing material, includes the following steps : an emission by N light sources of beams with wavelengths; an acquisition by M sensors, sensitive in at least one portion of the wavelengths; wherein M+N>3. The method also includes the steps of : calculating a first piece of information representing the diffusion, and a second piece of information representing the absorption, as a function of the signals and a piece of digital information representing the diffusing material as well as the sources and the sensors; calculating the water concentration in the sample as a function of the second piece of information.