The study focuses on the determination of the water-absorbing ability of the oxide of iron compounds by the method of pH-metry. It is shown that the process of wetting of a solid body depends on the mechanism of inhibition of acid-base interaction in the system "solid water" and predetermined by the type of functional groups naturally formed hydrate-hydroxyl cover. The study of acid-base interactions by pH-metry allows to obtain information on the express hydrophilize solid surface.