Aim: The purpose of this study was to determine the effect of optimum and acidic swimming pool water pH on the surface hardness and roughness of a high copper dental amalgam. Materials and Methods: Thirty disc shaped specimens of high copper dental amalgam (World-CapNon-Gamma-2) were prepared using split Teflon moulds. The specimens were divided into 3 groups according to the immersion water type; distilled water, optimum swimming pool water and acidic swimming pool water. The specimens were immersed for 768 hours. Surface hardness and roughness testing were performed before and after specimens' immersion. Results: Surface hardness results showed that the significantly lowest values were possessed by the specimens immersed in both swimming pool water pHs. On the other hand, significant increase in surface roughness was obtained in all specimens immersed in the different water types. Conclusion: Swimming pool water of different pH negatively affects the surface hardness and roughness of a high copper dental amalgam.