One of the most important treatment processes in surface water treatment is coagulation. Surface waters such as rivers and lakes contain suspended particles and turbidity. With the aid of coagulants, and by flocculation process, followed by sedimentation and filtration, these impurities can be removed from raw waters. Besides conventional chemicals such as alum and ferric chloride, polymers such as sulfonated polystyrene are getting common. In this study, we are interested in waste plastics; waste polystyrene-containing additives were converted into a polymeric flocculant by chemical modification. Specifically, waste polystyrene consisting of white coffee cups was sulfonated to produce a water-soluble polymer. The sulfonation was characterised by FTIR technique and the degree of sulfonation was determined by titration. The polymer provides high purification of the supernatant after flocculating a kaolin suspension. Moreover, the material provides a pure supernatant in the treatment of actual wastewater comparable to conventional polymeric flocculants. A new reclamation technology to convert waste plastic into a functional polymer is reported.