Ferric chloride and alum are the two coagulating substances, which are used for the elimination of organic matters and turbidity of water. The power of coagulation and suitable pH range of ferric chloride is more than alum. However, the concern and precaution about the use of ferric chloride is its severe corrosiveness. In this work, alum and ferric chloride were used as coagulating matters for Isfahan and synthesized water. The corrosion rate of copper in synthesized water containing chloroform for adjusting the organic material concentration in water with the added concentrations of coagulating material in there different pH were evaluated. In addition, the corrosion rate of copper in Isfahan water containing different concentrations of coagulating matter were investigated. The results indicated that the water with pH=6.5 had an optimum concentration 4 ppm for ferric chloride, which was equivalent to 6 ppm for alum. In pH=7.5, the optimum concentration was 6 ppm for ferric chloride which was equivalent to 12 ppm for alum. In pH=9, the optimum concentration was found to be 12 ppm for ferric chloride which was equivalent to 24 ppm for alum. An optimum concentration of ferric chloride is a concentration in which the corrosion rate of copper in water is qual or even less than that in the equivalent concentration of alum. In Isfahan water in pH=7, the optimum concentration of ferric chloride is 5 ppm which is equivalent to 10 ppm of alum.