Separation of heavy metals from water may be done by sulphide precipitation. In order to make the metal sulphides more valuable for reuse, they should be as pure as possible. To separate the metals from each other during the precipitation process different parameters as pH, sulphide concentration and redox potential may be controlled. Adjustment of the redox potential to specific values results in separation of copper from cadmium even at the same pH. In the copper precipitation step 98.7 ± 0.5% was precipitated and the remaining part was transferred to the cadmium precipitation step where 0.7 ± 0.5% of the copper precipitated. The main part of cadmium (95.6 ± 1.3%) was precipitated in the second step. These results show that it is possible to separate copper from cadmium by the use of redox potential control.