Then comes aluminum sulfate. It causes particles to stick together, or coagulate. Larger, heavier particles form through flocculation. Pumped into filtration tanks, the water is purified by filters of anthracite and sand. Carbon may be used if the water has a fishy odor or taste.
Lime renders the water slightly alkaline.
This makes it easier on the system's iron pipes and less likely to leach lead or copper out of household pipes. The water also gets a dose of fluoride, used since 1949, and a final bit of chlorine. The water is tested at every stage to monitor its quality. Finally, it is pumped into huge clearwells, underground storage tanks. The eight at Franklin hold a total of 48 million gallons.