Provided is a process for the removal of metal ions from water which comprises filtering the water through a bed or layer of granular lightburned or hardburned magnesium oxide. The use of granular hardburned or granular lightburned grades of the magnesium oxide provides one with a most effective process for the removal of metal ions, as well as a process which permits a greater throughput of water before the effectiveness of the magnesium oxide decreases substantially.The process of the present invention also involves an acidic backwash to regenerate the granular magnesium oxide. The acidic backwash is used to strip the captured metal ions from the surface of the granules, and has been found to be quite effective. The acid is generally a dilute acid, e.g., about 1 to 10 percent by weight acid concentration.