Aluminum sulfate is used in water purification and as a mordant in dyeing and printing textiles. In water purification, it causes impurities to coagulate into larger particles and then settle to the bottom of the container (or be filtered out) more easily. This process is called coagulation or flocculation. Research suggests that in Australia, aluminum sulfate used this way in drinking water treatment is the primary source of hydrogen sulfide gas in sanitary sewer systems.