In this paper, we demonstrated the viability of recycling waste plastic cups for synthesizing polystyrene sulfonate (PSS), which was used as an auxiliary agent of coagulation, flocculation and flotation in water and wastewater treatment plants. The study was carried out in the treatment plants of the Municipal Department of Water and Wastewater in Uberlondia-MG, Brazil. The polystyrene sulfonate, when compared with commercial polymers, presented promising results for treating water with turbidity above 30 NTU, and presented the best results on the wastewater treatment. However, for water treatment, a further study needs to be carried out considering the Brazilian legislation concerning the quality of the treated water.