Water treatment is necessary to remove substances that can bring harm to the health os the population. In the complete cycle treatment plants, the chemical coagulants are used in the clarification step, generally with the presence of aluminum and iron salts, for example Aluminum Polychloride (PAC). The process can be expensive because the chemical coagulants generate residuals after being used, so one way to avoid the impacts is the choice of organic coagulants as aids in coagulation. In this context, the objective of the research was to analyze the efficiency of the organic coagulant Tanfloc SG as an auxiliary of the PAC in the treatment of raw water of the Santo Anastácio river. The analyzes showedthat the parameters in the water after treatment did not reach the expected objective, and new analyzes are necessary to identify the ideal use of the organic coagulant Tanfloc SG in the water treatment of the Santo Anastácio river.