Abstract: The capability of modifying synthetic resin (MSWPS) prepared from waste polystyrene plastics to remove hardness and some inorganic pollutants from synthetic hard water was investigated in this study. The waste polystyrene (WPS) was prepared from the foam of food packaging and white coffee cups, and then active adsorbent cationic resin was synthesized from them, forming sulfonated waste polystyrene (SWPS). The first preparation for hard water was made by dissolving MgCl2 or CaCl2 salts in deionized H2O (DW) and passing it through SWPS resin to study the performance evaluation of the flow rate (mL/min), resin dosage (g), temperature (oC) and pH on the removal percentage of calcium, magnesium, and total hardness from this hard water.