Ion exchange in a fluidized bed has been shown to be an effective design for anion and cation exchange. However, little is known about combining anion and cation exchange resins in the same vessel. More specifically, can combined ion exchange be predicted by adding the removal of anions during anion exchange to the removal of cations during cation exchange? Results indicated that combined ion exchange can reduce precipitation of sparingly soluble minerals, such as CaCO3, in the bulk solution by simultaneously removing calcium and bicarbonate. Inorganic cations dominated the ion exchange behavior during these processes, and organic anions such as dissolved organic matter (DOM) behaved the same in combined ion exchange as in anion exchange. Results showed that it is possible to estimate sulfate and magnesium removal during combined ion exchange by rules of superposition, as well as calcium when initial concentration of calcium is low. Synthetic waters with varying divalent cations were compared to a natural groundwater, both of which had low organics and high divalent cations. Results showed similar behavior between natural and synthetic waters with varying types of DOM. The effect of combined ion exchange on separation factors is also calculated and discussed. (C) 2013 Elsevier B.V. All rights reserved.