This research evaluated the combined ion exchange (CIX) process to give drinking water treatment plants a new option for multi-contaminant removal. The CIX process uses anion exchange resin and cation exchange resin in a single vessel, which enables simultaneous removal of anionic and cationic contaminants. The novel aspect of the CIX process investigated in this research was its application in a pilot-scale, completely mixed flow reactor (CMFR) with resin recycle and resin regeneration thereby providing realistic performance data. A wide range of contaminants was tested for removal including dissolved organic carbon (DOC), calcium, strontium, nitrate, sulfate, sodium, and chloride, and sodium chloride (NaCl) and potassium bicarbonate (KHCO3) were compared in terms of regeneration efficiency. The key results showed 50 to 80% removal of DOC, calcium, strontium, and sulfate, and less than 30% removal of nitrate, sodium, and chloride. In general, NaCl and KHCO3 showed similar regeneration efficiency. Removal of sodium and chloride by CIX was only possible when KHCO3 was used for regeneration due to the potassium and bicarbonate counterions.