Phreeqc was used to calculate the calcium carbonate precipitation potential(CCPP) of Huangpu river water. The possible reasons for the differential between calculated and experimental CCPP were firstly analyzed. Furthermore a statistical analysis was made to study the correlation between pH and CCPP of the raw waters. The results show phreeqc, a free open -source program, has similar high level of calculation accuracy with other commercial software. The difference of CCPP values between experimental and theoretical calculation are considerable, which is mainly due to the lack of water indexes. With a statistical analysis, the correlation between pH and CCPP of Huangpu river water was found. The chemical stability of raw water could be achieved by adjusting the calculated CCPP to be 0~4 mg/L CaCO 3 and the experimental CCPP to be 0~4 mg/L CaCO 3.