Our studies suggest a cheap and simple way to decontaminate two ligand-containing rinsing waters of metal finishing. Both copper diphosphate and acidic zinc ammonium containing rinsing wastewater may be decontaminated by mixing, which results in precipitation of solid solution of potassium, ammonium, copper, and zinc diphosphates. About 80-99.5% of environmentally hazardous substances, viz. zinc, copper, and diphosphate are removed from the solution. Chemical and phase composition of the precipitate was examined. We have also suggested several possible ways to utilize the precipitate. This way of decontamination requires no expensive reagents since only a small amount of H2SO4 is required for pH adjustment.