The possibility of using waste polystyrene,to remove the hardness of water has been investigated. Waste of polystyrene is consisting of white coffee cups and they were converted into adsorbent by heterogeneous sulfonation. Infra red technique has been used to confirm the sulfonation. Degree of sulfonation and cation exhange capacity have been determined by titration. Hard water has been prepared by dissolving Mg or Ca salts in distilled water. The modified polymer provides high purification of hard water comparable to conventional adsorbent.