Ammonium is one of the objectionable constituents in drinking water and water supply reservoirs. Removal of ammonium from water supply resources is sometimes necessary for acceptable drinking water quality. Ion exchange with the ammonium selective natural zeolite clinoptilolite, is proposed as one possible option for this purpose. The capacity and success of clinoptilolite for ammonium removal under those conditions have been investigated. The results from both batch isotherm experiments and continuous column runs have shown that the process is indeed effective. However, the competing ions mostly in the form of hardness impact with the potential capacity significantly. Depending upon conditions prevailing, over 50% of the capacity may be used by the competing ions, reducing the capacity intended for the targeted ammonium ions, however the limits for ammonium for drinking water could be achieved under all circumstances without problems.