a method of removing toxic compounds from water comprises the steps of providing a polymeric ligand exchanger having a chelating resin containing nitrogen electron donor atoms and a transition metal ion bonded with the nitrogen donor atoms on the surface of the chelating resin , and contacting water containing a toxic compound with the polymeric ligand exchanger to remove the toxic compound from the water . the preferred metal ion is a cupric ion , and the preferred toxic compound to be removed from water is arsenic . the method further includes the step of regenerating the polymeric ligand exchanger with brine and the step of treating the brine used to regenerate the polymeric ligand exchanger with iron chloride to remove arsenate therefrom so that the brine may be re - used in the system to reduce the overall volume of waste material .