Monochloramine as a Drinking Water Disinfectant


Drinking water drawn from surface water sources such as Lake Champlain must be disinfected to kill bacteria, viruses and other organisms that can cause serious illness and death. The Environmental Protection Agency (EPA) requires that public water systems use chlorine at specified levels for “primary” disinfection at the water treatment facility.

“Secondary” disinfection is also required to treat any type of contamination that could occur after the water leaves the treatment plant. EPA approves three disinfectants for use as a secondary disinfectant: chlorine, chlorine dioxide and monochloramine.

Monochloramine is a chemical that is made by combining chlorine with ammonia. Although it is a weaker disinfectant than chlorine, monochloramine is more stable, remains effective in the water system over longer distances for a longer period of time, and forms lower levels of regulated disinfection byproducts than chlorine.

Monochloramine has been used in the U.S. as a secondary disinfectant since the 1930s. While the EPA does not know the absolute number of people who are using water treated with monochloramine, it is estimated that the number exceeds the 68 million who were identified in a 1998 survey. In New England, more than 3 million people in 135 communities are served by monochloraminated water.

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Review of Scientific Literature

The Vermont Department of Health has been reviewing the history, science and potential health risks associated with the use of monochloramine, and conducted an extensive new review of all available scientific literature on the subject.

The Health Department has determined that the use of monochloramine as a secondary disinfectant is not likely to result in adverse health effects. On the contrary, the Health Department believes that the use of monochloramine will reduce the concentration of regulated and possibly unregulated disinfection byproducts in drinking water. This reduction may contribute to fewer adverse health effects compared to drinking water treated with free chlorine as a secondary disinfectant.

All available research at this time still supports the EPA conclusion in its 1994 review, Drinking Water Criteria Document for Monochloramine, that: “In humans, health effects do not appear to be associated with levels of residual monochloramines typically found in drinking water.” However, there still remain gaps in the data regarding the health effects of all water disinfectants.

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History of Monochloramine Use in Vermont

In April 2006, the Champlain Water District (CWD) switched from chlorine to monochloramine as an alternative for secondary disinfection of its 12 municipal systems that serve nearly 68,000 people in Chittenden County. Burlington has a separate water utility that does not use monochloramine.

Municipalities served by the Champlain Water District:

The Health Department consulted with the Vermont Department of Environmental Conservation to review the Champlain Water District’s engineering and monitoring plan to be sure it was in full compliance with EPA regulations.

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Review of Health Concerns

Since the Champlain Water District began using monochloramine in April 2006, the Health Department has heard repeatedly from a number of people about health complaints they relate to monochloramine in their water.

Health Department officials began meeting with representatives of anti-chloramine groups and the Champlain Water District to better understand concerns, and provided testimony to the Vermont Legislature. In addition, Health Department medical and toxicological experts have spoken personally with many people who have called with health concerns, and continue to review all available scientific articles and studies.

To date, the Health Department has found no credible evidence to show that the use of monochloramine to disinfect public water is a threat to public health or has been associated with adverse side effects. However, we know that there are individuals who have symptoms that have not been diagnosed or treated, and that it is possible that these are related to monochloramine. We continue to encourage anyone with health of medical concerns to contact their health care provider.

The Health Department has not been able to rule out disinfectants as possible contributing factors to health concerns expressed by some Vermonters despite the long history of their use, apparent safety, and lack of documented health issues among the many thousands of Champlain Water District customers.

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Health Care Provider Survey

In April 2007, the Health Department surveyed 173 health care providers in Chittenden County to try to find out if there is a hidden prevalence of health problems related to monochloramine now used by Champlain Water District.

Those surveyed included family practice and primary care physicians, pediatricians, pulmonologists, dermatologists, allergists and naturopaths. Of the 81 health care provider surveys returned, two providers reported having a patient whose underlying disease was exacerbated by the water, 11 providers reported they were not sure if patient complaints were related to the water, and 59 providers reported the water did not cause patient complaints.

The Health Department continues to encourage anyone who has health problems that may be related to monochloramine to contact their health care provider and share their concern.

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CDC Site Visit and Report

In response to continuing questions about monochloramine use, the Health Department invited a team of public health and drinking water experts from the Centers for Disease Control & Prevention (CDC) to come to Vermont to listen to the concerns of all involved.

On September 26, 2007, the Health Department hosted the CDC team in a series of meetings with state health and environmental officials, lawmakers and advocates. From Sept. 26-28, CDC experts also visited people in their homes and conducted telephone interviews with people who have expressed personal health concerns.

CDC is not planning a study or an investigation at this time. The purpose of this site visit was to listen to Vermonters’ concerns about monochloramine. From the information gathered in Vermont, the CDC may provide future guidance on this issue to the Health Department and other communities nationwide.

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