Oxidizable for organic and/or inorganic compounds in waters are subjected to catalytic degradation using a catalyst applied to an oxygen-storing inert carrier, for example of graphite, coke, a non-gassing coal or active carbon. The carrier used is coated with a cationic dye complexed with heteropolyacids and/or polyacids and/or salts or metal acids of subgroups V to VIII.The advantages of the process include the prevention of biological growth on the catalyst surface by the biocidal dye cation and the avoidance of calcium and magnesium deposits on the catalyst surface through the presence of the cationic solid.