In many chemical reactions water plays an important role as a solvent, a reaction partner or a catalyst. At high temperatures water tends to be an extremely reactive partner. In order to investigate the synthesis potential of hot water in near- and supercritical conditions, the conversion of acetonitrile and benzonitrile (representing aliphatic and aromatic nitriles, respectively) was examined in near- and supercritical water in the temperature and pressure ranges of 300 to 450 degrees C and 23 to 32 Mpa. The investigations showed that nitriles convert selectively to the corresponding amides and carboxylic acids in hot water without any additives, such as mineral acids and salts.