Water Distribution Systems:The New Frontier In Protecting Public Health

The water distribution system is alive and breathing. Historically the major focus of Environmental Protection Agency (EPA) regulations has been on the water treatment plant - improving...

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The water distribution system is alive and breathing. Historically the major focus of Environmental Protection Agency (EPA) regulations has been on the water treatment plant - improving its performance relative to removing and inactivating microorganisms, and removing particles and harmful chemicals or precursors to various by-products. Those measures have been quite effective at improving water quality and reducing public health risks. The latest round of regulations continues with that approach to further stretch the limits of water treatment technology.

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Percent waterborne outbreaks in community water systems 1971-1998 (294 outbreaks)
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The next round of regulations will turn its focus to the distribution system - the final barrier to protecting water quality before it reaches the consumer. We now know that the piping system is a living, breathing biological and chemical reactor. The conditions are not sterile, nor are they static. Microbes are growing and continually sloughing off, and chemical reactions and corrosion proceed after the water leaves the treatment plant.

Public health experts have indicated that 30 percent of recent waterborne outbreaks were attributable to distribution system deficiencies. As the number of outbreaks attributable to treatment continues to decrease, the percent of those linked to distribution system deficiencies will likely increase.

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EPA is gathering technical information as a prelude to future rulemaking that will affect the distribution system. The actions being considered include revising the Total Coliform Rule and/or developing a Distribution System Rule. As part of the information-gathering efforts, EPA has developed a series of white papers describing the status of what is known on the following subjects:

  • Cross-connections and backflow
  • Intrusion of contaminants from pressure transients
  • Nitrification
  • Permeation and leaching
  • Microbial growth and biofilms
  • New or repaired water mains
  • Finished water storage facilities
  • Water age
  • Deteriorating buried infrastructure

(The papers are available for download from the EPA’s website at: http://www.epa.gov/safewater/tcr/tcr.html#distribution.)

At EPA’s request, the Water Science and Technology Board of the National Research Council conducted a preliminary assessment of distribution system risks to public health. They identified the following priorities:


  • Cross-connecitons and backflow
  • New and repaired water mains
  • Finished water storage
  • Premise plumbing
  • Distribution system operator training


  • Biofilm growth
  • Loss of residual via water age and nitrification
  • Low pressure transients and intrusion

It is interesting to note that the industry already knows a tremendous amount about four out of the five high priority items, the only exception being “Premise plumbing”. We know how to administer and implement cross-connection control programs, how to maintain sanitary conditions while repairing and installing mains, how to operate our storage facilities with water quality in mind, and how to train operating staff. However, many utilities are not following best management practices in these areas and need to review their operations. Very few utilities have good documentation of their operating procedures related to the distribution system. Further, we need to research and understand the effects of premise plumbing on water quality at the consumers’ taps.

Research is ongoing on several fronts. The American Water Works Association Research Foundation (AwwaRF) and others are trying to fill in the knowledge gaps to help form the basis for these new rules.

For example, HDR is conducting an “Assessment of Inorganics Accumulation in Drinking Water System Scales and Sediments” as part of an AwwaRF project that will focus on arsenic and radium accumulation and release from the distribution piping. HDR is also conducting an AwwaRF Project entitled “Strategy to Manage and Respond to Total Coliforms and E. coli in the Distribution System.” The objective is to develop a comprehensive set of guidelines to help utilities evaluate, manage and respond to positive coliform events in the distribution system. The company is also filling in research gaps by conducting several investigations on metal release from premise plumbing systems and entry into the drinking water.

Utility-based organizations are leading the way in bettering distribution system operations. AWWA has prepared and adopted a new and different type of standard, Distribution Systems Operation and Management, ANSI/AWWA G200-04, that offers a guide to best management practices for distribution systems. It is programmatic in nature unlike most standards, which are product-based.

AwwaRF recently published a project report, “Distribution Systems Water Quality Optimization Plans,” that provides case studies and templates to improve water quality, and contains more than 120 documented “Best Management Practices” related to the distribution system that are ready for use by utilities.

So what can you do? There are several things you can do now to get ready for future distribution system oriented regulations. These actions include:

  • Reviewing the white papers mentioned above to get some background on the technical basis for forthcoming regulations;
  • Continuing to track AwwaRF research on distribution systems;
  • Embracing the AWWA standard G 200-04, Distribution Systems Operation and Management;
  • Documenting the operating procedures for your distribution system along the lines that have been done for treatment facilities;
  • Conducting operations monitoring to better understand how system operations are affecting water quality; and
  • Looking at your cross-connection control program to see if it is operating efficiently.

About the Author:

Gregory Kirmeyer, P.E., is HDR’s national director of drinking water. He has more than 28 years of industry experience primarily related to drinking water quality. He may be contacted via e-mail at g.kirmeyer@hdrinc.com.

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