Cosmetic Alum is also used in purification of drinking water in industries. In a loading tank, some alum (phitkari) is added to the water so that the negatively charged light colloidal parts stick together and get heavy (flocculate) when alum makes the colloidal particles neutralized by making its aluminum ions get loaded with the colloidal parts. When the colloidal parts get heavy they can be easily separated from the tank for further chlorination of water in the process of purification of water.
Potassium alum is the common alum of commerce, although soda alum, ferric alum, and ammonium alum are manufactured.
Alums are useful for a range of industrial processes. They are soluble in water have an astringent acid, sweetish taste, react acid to litmus and crystallize in regular octahedron. When heated they liquefy and if the heating is continued, the water of crystallization is driven off, the salt froths and swells and at last an amorphous powder remains.