For the past 20 years, the US government has been implementing drinking water regulations with the intent of reducing the health risks associated with drinking water. Regulations have focused on the removal of microorganisms, reduction of disinfection byproducts and reduction of the leaching of lead and copper from distribution piping. New regulations will, for the first time, place a limit on chlorine residuals in distribution systems. In view of these new regulations, many utilities are concerned about maintaining chlorine residuals high enough to control distribution biofilms. The possible impacts of increased microbial growth resulting from phosphorus-based corrosion inhibitors is also a concern. This paper discusses the interactions among pipe materials, disinfectants, corrosion inhibitors, organics and distribution system biofilms in order to provide information on how treatment changes may affect biofilms.