This research aims to test the use of aluminum sulfate prepared from kaolin from Nawan, Al Baha, KSA, in the treatment of the surface water of the Al Ahsaba Dam. The analyses proved that the kaolin sample was pure and was successfully converted to amorphous metakaolin by calcination at 800 °C. Approximately 60% of alumina was extracted from metakaolin by dissolving hydrochloric and nitric acids separately. Aluminum sulfate was also separated from alumina dissolved in acids and its chemical composition was determined by analysis. The chemical changes that occurred in kaolin after calcination and in metakaolin after dissolution with acids were traced using different analytical techniques, such as TGA, XRD, FTIR, and SEM-EDX. Aluminum sulfate was used as a coagulant in the water of the Al Ahsaba dam to remove suspended solids. The chemical properties of the Al Ahsaba dam water were also tested before and after adding the prepared and industrial aluminum sulfates, such as turbidity, residual aluminum, hardness, electrical conductivity, and total dissolved solids, and compared to a sample of commercial drinking water. The results showed that aluminum sulfate prepared from kaolin Nawan is suitable for use in dam water treatment as a coagulant to remove suspended solids to supply treatment plants with the water needed to complete other treatment processes.