The water softener removes which ions from the dialysis water?

• A. Calcium and Magnesium
• B. Sodium and Potassium
• C. Chloride and Bicarbonate
• D. Phosphate and Sulfate

Answer: (A)

Hardness in dialysis water comes from calcium and magnesium ions. A water softener uses an ion-exchange resin that is preloaded with sodium ions. When hard water passes through, calcium and magnesium ions cling to the resin and are swapped for sodium (and sometimes potassium) ions. This removes Ca2+ and Mg2+ from the water, reducing hardness and helping prevent scale on dialysis equipment and membranes. The ions being replaced are the ones added to the water, so sodium and potassium aren’t removed by the softener—they’re the ions released into the water. The softener targets cations; chloride, bicarbonate, phosphate, and sulfate are anions and aren’t the priority removals here. So the ions removed by the softener are calcium and magnesium.