A device for reducing the content of polluting and/or unwanted substances in water, including a support made of polymeric material for a catalyst of the reaction of degradation of inorganic salts into gaseous substances; the catalyst, intended to reduce the energy required for the activation of the reaction and to accelerate its course, is an enzyme preferably selected from the group of lyases, and even more preferably selected from the subgroup of carbonic anhydrases. The inorganic are being carbonates, and/or hydrogen carbonates of calcium and/or magnesium, the reaction being the reaction of decarboxylation and acting for the conversion of inorganic salts into carbon dioxide and water according to the following reaction: HCO3−+H+H2O+CO2.