Poly Aluminium Chloride (PAC) solution is a chemical compound that is widely used in the water treatment industry. It is an inorganic polymer coagulant that is formed by the reaction of aluminum hydroxide and hydrochloric acid. The chemical formula for PAC is Aln(OH)mCl3n-m, where n represents the degree of polymerization and m represents the number of hydroxyl groups.PAC solution is usually available in liquid form, with a light yellow to dark brown color, depending on the concentration of the solution. The solution is highly soluble in water and has a slightly acidic pH value. The PAC solution is commonly used in the treatment of wastewater and drinking water to remove suspended solids, organic matter, and other impurities.