By Kelly A. Reynolds, MSPH, Ph.D.

Hundreds of boil water notices are issued in the United States each year in response to known or suspected municipal treatment failures or source water contamination events. Increased rainfall, flooding and an aging and potentially vulnerable infrastructure are primary reasons for drinking water contamination and boil water advisories.

The following is a summary of key management and response considerations should a boil water notice be issued in your community.

What are boil water notices? Who is at greatest risk?
Most boil water advisories are issued as a result of occasional treatment or distribution malfunctions in the municipal water supply and generally as a precaution until further testing can be done to indicate that the water is indeed safe for consumption. Water quality testing can take 24 hours to complete and thus the inconvenience to the consumer may be significant, impacting the confidence they have in the water supply facility.

Typically, notices are issued via media outlets (television, newspapers, radio) or flyers in the mail. For smaller communities, it is not uncommon for notices to be hand delivered while high-risk facilities (i.e., day care centers, nursing homes and hospitals) may be phoned directly. Whatever the format of the boil water notices, the content is generally the same. Consumers are advised to vigorously boil all water for one to two minutes that is used for for drinking, cooking, washing foods, bathing, brushing teeth and making ice, until further notice.. Alternatively, a purified or bottled-water source is often suggested.

Populations most at risk are the very young, very old and others with compromised immune function (i.e., HIV/AIDS, cancer chemotherapy and bone marrow transplant patients). These sensitive populations are known to have a risk of illness or death following a waterborne infection up to 100-1,000 times greater than the general population. In such cases, additional precautions to prevent exposure risks are warranted. Although it is recommended that populations at greater risk for waterborne disease routinely utilize a purified drinking water source, many continue to rely on tap water to meet their daily needs.

Indicators of compromised water
Coliform bacteria are routinely used to monitor drinking water quality and treatment efficacy in the US. E. coli is the coliform bacteria most commonly surveyed to indicate possible fecal contamination of drinking water. If E. coli is found in drinking water, additional tests are required and a boil water advisory is considered. There may be a significant lag time however between the first indication of impaired water and public notification or a targeted action plan.

Boil water notices are not issued lightly and generally result in serious implications for the community. The subsequent monitoring, treatment, informational dissemination needs and other related interventions can cost a community millions of dollars. Whether or not a boil water notice should be issued is debatable given that monitoring data is not necessarily a good indication of public health risks.

Positive results do not necessarily indicate the viability of the targeted organism. Often boil water notices are only issued when evidence of disease is reasonably indicated in the community and when that disease can be traced to a water source. Other red flags are when weather or disaster events have recently occurred (i.e., flooding, hurricanes, etc.), or when known compromises have occurred in the distribution system (i.e., main breaks, cross connection leaks, etc.) or when the treatment train is interrupted (a detected breach in the disinfection/filtration system or other system).

Recently, two Ontario communities issued boil water notices due to evidence of Giardia contamination, a human pathogenic protozoa. Although one community was experiencing an excessive amount of disease (considered an outbreak), the other was not.

In the latter case, Giardia was only found in 2/41 subsequent samples taken. Despite this low level of positive results, a boil water notice was in effect for a year in that community. This is an example of how pathogen-monitoring data can lead to false alarms, where the presence of a detectable pathogen in the finished water does not necessarily indicate an outbreak and, in fact, may be a low or acceptable level of risk.1

Compliance considerations
Despite awareness of a problem with drinking water, it is not uncommon to document noncompliance with public health warnings related to water quality. Following an event where a water main broke and was known to be impacted by sewage, residents were informed within hours of the event that water should be boiled prior to consumption.2

Notices were delivered by hand to the 878 households in the compromised distribution network. Surveys indicated that despite receiving the notice and understanding the warnings in place, 81 percent (n=350) of households reported engaging in activities likely to increase their risk of exposure to waterborne pathogens (i.e., brushing teeth, washing uncooked foods, forgetting to boil drinking water, washing dishes, etc.).

Noncompliance with respect to boil water notices can lead to serious health outcomes. Following a large waterborne outbreak in Missouri, 650/1100 residents were ill, 15 hospitalized and seven died from exposure to Salmonella bacteria in an unchlorinated community water supply.Researchers showed that there was a high rate of noncompliance with the boil water notice.3

In this particular outbreak, seven cases of Salmonella gastroenteritis were reported to the state health department on November 21, with the initial cases occurring on November 12. By early December, school absenteeism in the region increased by 250 percent and sales of anti-diarrheal medicines increased by 600 percent. By the end of December, 15 patients were hospitalized with Salmonella infections.

On December 28, approximately five weeks after the first identified cases, notices were sent to households with detailed information of the seriousness of the outbreak and the boil water advisory. Of the households surveyed, 31 percent had members that drank unboiled water, even though 91/92 of the homes surveyed said they were aware of the boil water advisory. Reasons cited for noncompliance included “not remembering” (44 percent) and “disbelieving” (25 percent).

Effective treatment
Conflicting reports as to how long water should be boiled to eliminate the risk of harmful microbes may contribute to the noncompliance issue. In most cases, boiling for one minute is effective for reducing the risk of common waterborne disease agents, such as Cryptosporidium, E. coli or rotavirus. Often a two-minute time is suggested.

Some feared bioterrorism agents, however, require much longer treatments. For example, Bacillus spores (the bacteria that causes anthrax) are reported to require up to 12 minutes of boiling to be inactivated.4

Advanced, point of use water treatment devices, with microbial removal/inactivation technology (i.e., reverse osmosis, ultraviolet light, etc.) are often designed to protect the consumer in the event of a disaster. The Centers for Disease Control (CDC) have issued guidance materials for hospitals, dental offices, nursing homes and other healthcare establishments following disruption of the water supply.

Once a boil water notice is rescinded, it is a good idea to flush all fixtures of the previously compromised water. Although targeting sensitive populations, the following recommendations can also be adapted by the general public in the home and in businesses.

According to the CDC5, after the boil water advisory is rescinded:

  1. Flush fixtures (e.g. faucets, drinking fountains) and equipment for several minutes and restart.
  2. Run water softeners through a regeneration cycle.
  3. Drain, disinfect and refill water storage tanks if needed.
  4. Change pre-treatment filters and disinfect dialysis water systems.

Proper maintenance of even the best POU systems, must be practiced to prevent exposure to harmful microbes, especially following a challenge event. In the end, many more boil water notices can be expected in the US.

Some will be false alarms while others will be necessary and life saving recommendations. All notices should be taken seriously.


  1. Wallis et al., (2001) Application of monitoring data for Giardia and Cryptosporidium to boil water advisories. Risk Analysis 21:1077-1085.
  2. O’Donnell et al., (2000) Effect of a boil water notice on behaviour in the management of a water contamination incident. Communicable Diseases in Public Health. 3:56-59.
  3. Angulo et al., (1997) A community waterborne outbreak of salmonellosis and the effectiveness of a boil water order. American Journal of Public Health. 87:580-584.
  4. Rice et al., (2004) Boiling and Bacillus spores. Emerging Infectious Diseases. Available from: vol10no10/04-0158.htm
  5. CDC (2003) Healthcare water system repair following disruption of water supply. Excerpted from the Guidelines for Environmental Infection Control in Health Care Facilities, 2003. Available at:

About the author
Dr. Kelly A. Reynolds is an associate professor at the University of Arizona College of Public Health. She holds a Master of Science degree in public health (MSPH) from the University of South Florida and a doctorate in microbiology from the University of Arizona. Reynolds has been a member of the WC&P Technical Review Committee since 1997. She can be reached via email at [email protected].




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