Organics matters including algae are the major contaminants of Nak-dong river and it`s concentration is more increasing now. The use of coagulants has been incresed for the effective treatment of drinking water, and aluminum coagulants have been the most widely used in raw water treatment. However, when inorganic metal coagulant is excessively used for long period, it would result in secondary problems, such as increasing sludge production, enhancing the cost of water treatment process, and increasing concentration of residual metal, especially aluminum. Therefore, recently, in order to reduce the use of metal coagulant and enhance the coagulation effectiveness, several alternative coagulants, such as polymeric inorganic coagulants and organic polymers, have been used in water treatment plants. The objectives of this research were (1) to determine optimum dosage concentration and compare the coagulation efficiency at various pH ranges with alum alone, alum+cationic polymer, and alum+anionic polymer, (2) to evaluate the amount of alum reduced by using organic polymer, (3) to maximize removal efficiency of organic matter and minimize the concentration of residual aluminum.