This paper presents a computer model to investigate the buffering function of aluminum being in equilibrium with mineral kaolinite in acidic natural water. Factors affecting the theoretical pH values are discussed. The model is verified by analyzing practical water samples. This paper presents a computer model to investigate the buffering function of aluminum being in equilibrium with mineral kaolinite in acidic natural water. Factors affecting the theoretical pH values ​​are discussed. The model is verified by analyzing practical water samples.