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Water: Total Coliform Rule

Distribution System

Drinking Water Distribution Systems

Water distribution systems consist of an interconnected series of pipes, storage facilities, and components that convey drinking water and meeting fire protection needs for cities, homes, schools, hospitals, businesses, industries and other facilities.  Public water systems depend on distribution systems to provide an uninterrupted supply of pressurized safe drinking water to all consumers. It is the distribution system mains that carry water from the treatment plant (or from the source in the absence of treatment) to the consumer.  Spanning almost one million miles in the United States, distribution systems represent the vast majority of physical infrastructure for water supplies.

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Water Quality and the Distribution System

New pipes added to distribution systems as development occurs, result in a wide variation in pipe sizes, materials, methods of construction and age within individual distribution systems and across the nation.  As these systems age, deterioration can occur due to corrosion, materials erosion, and external pressures that can lead to breaches in pipes and storage facilities, intrusion, and main breaks.  Deteriorating water infrastructure has resulted in frequent water main breaks, openings in storage tanks, water pressure fluctuation, and other situations that can pose intermittent or persistent health risks. 

Specific water quality problems can occur in the distribution system as a result of changes to the ideal operation of a system. Discussion of these potential problems is provided below.

  1. Distribution System Research and Information Collection Partnership Priorities
  2. National Academy of Sciences Committee on Public Water Supply Distribution Systems: Assessing and Reducing Risks 
    At EPA’s request, the National Academy of Sciences convened a committee to undertake a study of water quality issues associated with public water supply distribution systems. The Academy released two reports in 2005 and 2006. The reports and additional information on the study can be found at the NAS Web site.


  3. Distribution System White Papers  
    Note
    These papers present available information and do not represent Agency policy or necessarily reflect the views of EPA.

    The white papers on Buried Infrastructure and Intrusion were prepared by the American Water Works Service Company.

    Papers on Main Repair, Storage, Permeation and Leaching, Nitrification and Water Age were prepared by the American Water Works Association (AWWA).

    EPA worked with stakeholders and developed a series of "white papers" on distribution system issues ranked of potentially significant public health concern (see list below) to serve as background material for EPA, expert and stakeholder discussions.

Protecting Water Quality in Distribution Systems

EPA has promulgated regulations that pertain to distribution systems.  These are the Surface Water Treatment Rules (disinfectant residual and sanitary survey requirements), the Stage 1 and 2 Disinfectants and Disinfection Byproducts Rules (DBPR) (monitoring for DBPs in the distribution system), the Ground Water Rule (sanitary surveys), and the Total Coliform Rule (monitoring for bacterial contamination in distribution systems).

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