Some of the methods for the removal of ionic and nonionic impurities from water are still in use as alternatives to demineralization in certain applications. Also these processes are used as treatments prior to demineralization, either for reducing the ion exchange load on the resins, such as the lime pretreatment for the reduction of alkalinity, or for removing impurities that would foul and clog the resins, such as pretreatment and removal of color, turbidity, and organic matter.

The old methods of removing ionic impurities have certain limitations. They can remove only some cations or anions, whereas demineralizers remove all of them. Nevertheless, they continue in use because they are economical: The chemicals added are less expensive than the acid and caustic soda regenerants used for demineralization, and their doses are smaller. In many water purifying projects, the old methods are included as pretreatment, and the combinations results in lowest total operational cost.. This pretreatment allows the demineralizers to be used as a finisher and refiner.