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A Few Public Drinking Water Systems Violate Water Quality Standards


In my last post, I noted that there are 2,738 public water systems in Missouri. Federal and state laws require public water systems to monitor and test the quality of the water they provide to customers. Summary results are published annually by the Missouri Department of Natural Resources, and detailed reports are published by individual water systems.

A public water system is one that provides water to at least 15 service connections, or to an average of at least 25 people for at least 60 days each year. Community Systems (CWS) supply water to the same population year-round. Non-Transient Non-Community Water Systems (NTNCWS) supplies water to at least 25 of the same people at least 6 months per year, but not year-round. An example might be a school that has its own water system. A Transient Non-Community Water System (TNCWS) provides water in a place where people do not remain for long periods of time. Examples might include gas stations or campgrounds that have their own water systems.

The amount of treatment that water must receive differs depending on the source of the water. Surface water and underground water under the direct influence of surface water are more vulnerable to contamination, so they receive more treatment. Underground water from aquifers not under the direct influence of surface water tend to contain water that is heavily filtered by the rock through which it seeps. Sometimes, the seepage is so slow that the water is old, predating most forms of modern contamination.

Source: 2011 Annual Compliance Report of Missouri Public Drinking Water

Source: 2011 Annual Compliance Report of Missouri Public Drinking Water

The top graph at right shows the percentage of community water systems that meet all health-based requirements by year. The bottom graph shows the number of violations involving E. Coli or acute coliform levels. Non-compliance can result from many factors, from broken pipes, to human error, to systems that are inadequate in the first place. But the graph shows that compliance with all health-based regulations consistently ranges above 90%. The two exceptions were 2007 and 2010. The cause in 2007 was an error in backwashing a filter at the Missouri American Water Company South Plant in St. Louis County. The error caused a spike in turbidity that lasted four minutes. During that time the water reached an estimated 24,578 customers, though no reports of illness were associated with this event. In 2010, the problem involved “our largest supplier,” (Missouri American in St. Louis County again). The report states that it was a short-term event that affected few people, but the narrative is vague, and the violation is not included in the data tables.

The DNR monitors two broad kinds of violations. Water contaminants can exceed their respective maximum concentration levels, or a water system can fail to adequately perform and report  the testing required by law. The most common violation in 2011 was exceeding the maximum level of total coliform bacteria. Coliform bacteria are a class of many microorganisms that are widespread in the environment. Most do not represent a hazard to human health. Most of the violations were not acute. However, the presence of E. Coli, a specific type of coliform bacteria, or of an acute coliform violation is a sign the water may have become contaminated with fecal material, which carries many other bacteria that are hazardous to human health. Thus, the presence of E. Coli or of an acute coliform violation results in a boil order. Thirty-two water systems (1%) in Missouri received boil orders in 2011, some more than once, and the periods covered lasted from a few days to over a month. The systems are listed in Appendix A of the report.

Twenty-one water systems (<1%) had chemical violations, most often for trihalomethanes. These are water treatment byproducts. They form if disinfectants (chlorine, bromine) used to treat the water react with matter that may be present in the water (e.g. decaying vegetation).

Sixteen water systems (<1%) had violations involving excess radiological contaminants. This problem often involves radon, a radioactive substance that occurs naturally in the soil.

As the violations in 2007 and 2010 indicate, some of the violations can be quite brief, and the threat they represent to public health can be small. However, some systems experience repeated violations, and then the threat to public health increases. The DNR focuses its efforts on water systems that have a history of repeated contamination, and especially on those with a history of suspected contamination and a history of inadequate testing.

Forty-four water systems (1%) were listed as having had three or more major coliform violations and chronic monitoring violations. Many of them received repeated citations. They are listed in Appendix B of the report. In addition, 34 water systems (1%) were listed as having repeat monitoring violations. They are listed in Appendix C of the report.

Correction: The 16 radiological violations were most often caused by the level of combined radium, not radon. 6/2/14


2011 Annual Compliance Report of Missouri Public Drinking Water, Missouri Department of Natural Resources, Pub. 2449, http://dnr.mo.gov/env/wpp/fyreports/index.html.

Information regarding the violations in 2007 and 2010 was taken from the 2007 and 2010 versions of the report, available at the same web address.

Information on trihalomethanes from: Disinfection Byproducts: A Reference Resource, EPA, http://www.epa.gov/envirofw/html/icr/gloss_dbp.html.

Information on coliform bacteria: 5.11 Fecal Bacteria: What Are Fecal Bacteria and Why Are They Important, EPA, http://water.epa.gov/type/rsl/monitoring/vms511.cfm.


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