The objectives of this study were to determine: the relationship between the application of polyphosphate and chlorine residual level; the effect of polyphosphate addition on biofilm accumulation within the distribution system; the effect of polyphosphates on unlined cast iron and steel pipe tubercles; if the hydraulic capacity is increased after the addition of polyphosphates; if customer complaints due to color are reduced after the addition of polyphosphates; and, if customer complaints due to taste, odor and particles are reduced after the addition of polyphosphates. The polyphosphate addition started on November 6, 1998 in an isolated small area of the system and was expended on June 17, 1999 to approximately 3.6 mi2 in size. Pipe sizes in this area vary from 4-12 inches in diameter and material composition is approximately 50% unlined cast iron, 25% cement lined cast iron and 25% transite pipe. The study area is approximately 80% residential and 20% commercial and light industrial facilities. Includes 14 references, tables, figures.