Drinking Water Distribution Systems Assessing and Reducing Risks (2006) / Chapter Skim
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Pages 1-14
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Most regulatory mandates regarding drinking water focus on enforcing water quality standards at the treatment plant and not within the distribution system. Ideally, there should be no change in the quality of treated water from the time it leaves the treatment plant until the time it is consumed.
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The committee addressed tasks one and two in its first report, which is included as Appendix A to this report. The distribution system issues given highest priority were those that have a recognized health risk based on clear epidemiological and surveillance data, including cross connections and backflow; contamination during installation, rehabilitation, and repair activities; improperly maintained and operated storage facilities; and control of water quality in premise plumbing.
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Nonetheless, many of the report recommendations are relevant even if an alternative distribution system design is used. REGULATORY CONSIDERATIONS The federal regulatory framework that targets degradation of distribution system water quality is comprised of several rules under the Safe Drinking Water Act, including the Lead and Copper Rule (LCR)
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G200 has advantages over other voluntary programs, such as HACCP, in that it is more easily adapted to the dynamic nature of drinking water distribution systems. PUBLIC HEALTH RISK OF DISTRIBUTION SYSTEM CONTAMINATION Three primary approaches are available to better understand the human health risks that derive from contamination of the distribution system: risk assessment methods that utilize pathogen occurrence data, waterborne disease outbreak surveillance, and epidemiology studies.
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In general the identified number of waterborne disease outbreaks is considered an underestimate because not all outbreaks are recognized, investigated, or reported to health authorities. A third approach for estimating public health risk is to conduct an epidemiology study that isolates the distribution system component.
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Better public health data could help refine distribution system risks and provide additional justification for the prioritization. The following select conclusions and recommendations regarding the public health risks of distribution systems are made, with additional detail found in Chapter 3.
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hydraulic integrity, which refers to the maintenance of a desirable water flow, water pressure, and water age, taking both potable drinking water and fire flow provision into account, and (3) water quality integrity, which refers to the maintenance of finished water quality via prevention of internally derived contamination.
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Long detention times can also greatly reduce corrosion control effectiveness by impacting phosphate inhibitors and pH management. A final component of hydraulic integrity is maintaining sufficient mixing and turnover rates in storage facilities, which if insufficient can lead to short circuiting and generate pockets of stagnant water with depleted disinfectant residual.
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Water residence times in pipes, storage facilities, and premise plumbing should be minimized. Excessive residence times can lead to low disinfectant residuals and leave certain service areas with a less protected drinking water supply.
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. This issue is of critical importance in premise plumbing where long residence times promote disinfectant decay and subsequent bacterial growth and release.
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making some of the elements of G200 fall under existing federal regulations through the Government Accounting Standards Board, (2) state regulations that require adherence to G200 including building and plumbing codes and design and construction requirements, (3)
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Virtually every problem previously identified in the main water transmission system can also occur in premise plumbing. However, unique characteristics of premise plumbing can magnify the potential public health risk relative to the main distribution system and complicate formulation of coherent strategies to deal with problems.
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Changes in the plumbing code such as those considered in Canada and Australia that involve mandated mixing valves would seem logical to prevent both scalding and microbial regrowth in premise plumbing water systems. On-demand water heating systems may have benefits worthy of consideration versus traditional large hot water storage tanks in the United States.
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An epidemiological study to assess the health risks of contaminated premise plumbing should be undertaken in high risk communities.
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