The Information Collection Rule (ICR) was agreed to by water suppliers, environmental groups, consumer groups, and regulatory agencies. The data were collected from 296 public water systems each serving at least 100,000 people, from July 1997 to December 1998. These very large systems have invested collectively over $100 million to provide extensive new information on the occurrence of pathogens and disinfection byproducts, and on water treatment methods. The pathogen and disinfection byproduct data was collected from water systems that use surface water (e.g. lakes or rivers) or ground water under the influence of surface water. Disinfection byproduct data was also collected from water systems that use ground water. Bromate is required to be collected by only treatment plants that use ozone or chlorine dioxide as disinfectants. Chlorite is required to be collected by only treatment plants that use chlorine dioxide as a disinfectant. The information will be used together with other ongoing research to identify where improvements can be made, and to guide future regulations of these contaminants.