Mixing of near-neutral pH mine water and surface water substantially reduced the reactive portion of the natural organic matter (NOM) in the surface water by enhancing the coagulation process, using alum. The hardness and ionic moieties in the mine water improved the effectiveness of the alum in reducing the NOM concentrations. This is important because the presence of NOM can lead to the fouling of membranes and corrosion in the drinking water plant, and deteriorates drinking water quality by contributing undesirable changes in odor, taste, color. In addition, the presence of NOM can lead to carcinogenic by-products as a result of chlorination. The interactive effects of different operational conditions, i.e. pH, mixing proportion, and coagulant dose, were optimized using a statistical tool. The results affirmed that mixing of this mine water with river water would be an appropriate way to maximize the removal of the reactive part of NOM prior to disinfection and provide good quality drinking water.