We studied the suppression of pitting corrosion in copper tubes used for heat transfer in cooling water systems with absorption chillers. The corrosion was caused by the relation between the carbon film on the copper tube surface and the water quality flowing through the tube. Phosphonic acid and benzotriazole (BTA) were used as water treatment chemicals to suppress pitting corrosion. Silicate and calcium ions are effective for corrosion resistance of copper in the presence of phosphonic acid and BTA. In addition, we also studied the effects of chloride ions, known to have a corrosive effect, on copper pitting corrosion. In this study, hydrogen carbonate ions were added to these factors including phosphonic acid, BTA, silicate ions, calcium ions, and chloride ions, and the effects of hydrogen carbonate ions on copper pitting corrosion were investigated. As the hydrogen carbonate ion concentration increased, the number of sites of pitting corrosion decreased, and the potential decreased in the immersion test. Anode polarization curve measurements showed a tendency toward a parallel shift toward the cathode side. These results suggested that increasing hydrogen carbonate ion concentration resulted in greater inhibition of corrosion.