This work investigated the role of divalent metal cations (Mg2+, Ca2+, and Cd2+) and subsequent precipitation or complexation on decreased contaminant removal by bicarbonate-form anion exchange resin (AER-HCO3) relative to chloride-form AER (AER-Cl). The results showed that the removal of dissolved organic carbon and nitrate was lower for AER-HCO3 than AER-Cl, and contaminant removal by AER-HCO3 was affected by the presence of metal cation. For instance, magnesium and cadmium exhibited the greatest and least interference, respectively, with contaminant removal by AER-HCO3. The results suggested that precipitation was not the cause of decreased contaminant removal by AER-HCO3, and instead implied that complex formation between the contaminant and divalent metal was responsible for differences in removal by AER