2. Alum and Other Coagulants Aluminum sulfate, commonly known as alum, is used as a coagulant in the water treatment process. It helps to clump together small particles and impurities in the water, making it easier to remove them during sedimentation and filtration. Other coagulants, such as ferric chloride and polyaluminum chloride, may also be utilized depending on the specific requirements of the water source.