Drinking Water Advisories in Canada

Most boil water advisories issued in Canada between 2010 and 2012 were issued on a precautionary basis due to problems with drinking water equipment or processes. These problems accounted for 77% of boil water advisories in 2012, 75% in 2011, and 62% in 2010. By contrast, the presence of E. coli in drinking water samples accounted for 5% of boil water advisories in 2012, 6% in 2011, and 9% in 2010. Other water quality indicators, such as the detection of total coliform bacteria or unacceptable turbidity levels, accounted for 19% of boil water advisories in 2012, 19% in 2011, and 29% in 2010.

Causes of boil water advisories, Canada, 2010 to 2012

Causes of boil water advisories, Canada, 2010 to 2012

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How this indicator was calculated

Note: Data used in this indicator represent a sample of the Canadian population from a variety of agencies and jurisdictions across Canada. Given that the source of data is a relatively new surveillance tool, the data do not yet represent 50% of the Canadian population. "Other water quality indicators" include detection of total coliform bacteria and unacceptable turbidity levels in drinking water.
Source: Canadian Network for Public Health Intelligence, Drinking Water Advisories Application.

Drinking water advisories are public health protection messages issued by public health or regulatory authorities to inform consumers about actions they should take to protect themselves from real or potential health risks related to their drinking water supply. Advisories are generally precautionary, or issued before problems happen, and can take three forms: Do not consume, Do not use, and Boil water.

“Do not consume” and “Do not use” advisories are used when a chemical contaminant is suspected or confirmed in a drinking water supply. Both of these advisories are rare, representing approximately 1% of all drinking water advisories in Canada.

“Boil water” advisories are by far the most common type of advisory. They are issued when the microbiological quality of drinking water is suspected or confirmed to be compromised, meaning that disease-causing micro-organisms, such as bacteria, viruses or parasites, could be contained in the drinking water.

Most boil water advisories are issued because the equipment and processes used to treat, store or distribute drinking water break down or require maintenance. This broad array of reasons includes issues such as broken water mains, planned system maintenance, power failures or equipment problems. In other cases, extreme weather or heavy rains may cause the quality of surface or ground water sources to temporarily worsen, challenging the drinking water treatment system. Boil water advisories issued for equipment- and process-related reasons are generally issued before any actual decline in drinking water quality and are in place until conditions return to normal.

The presence of Escherichia coli, commonly called E. coli, signals the possible presence of other disease-causing microbes, such as Cryptosporidium, Giardia (which causes giardiasis, more commonly known as beaver fever), and viruses. E. coli is naturally found in the digestive system of all warm-blooded birds and animals, including humans, and is commonly found in water in the environment. Its presence in treated drinking water indicates recent fecal contamination by, for example, raw sewage or manure. E. coli can cause stomach illness along with other, more serious health problems. The detection of E. coli in drinking water also informs water-system operators that there may be other bacteria, viruses or parasites in the system, and may lead to a boil water advisory.

Other water quality indicators provide more information on drinking water quality and help identify changing conditions inside the drinking water system, but do not represent a health risk to consumers. These indicators include total coliform bacteria and turbidity. Total coliforms are a broad family of bacteria commonly found in the environment and turbidity is a measure of the cloudiness of water caused by particles. When unusual or elevated levels of these water quality parameters are measured in the drinking water system, the cause is investigated and the findings may contribute to the decision to issue a boil water advisory.

Community size and drinking water advisories

In 2012, 77% of boil water advisories were issued for drinking water systems serving 500 people or less. Systems serving fewer than 500 people received 78% and 80% of boil water advisories in 2011 and 2010, respectively.

Boil water advisories by community size, Canada, 2010 to 2012

Boil water advisories by community size, Canada, 2010 to 2012

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How this indicator was calculated

Source: Canadian Network for Public Health Intelligence, Drinking Water Advisories Application.

Boil water advisories are issued more commonly in small communities because of the unique challenges they face, including limitations to their operational capacity. For example, a broken water main in a larger city is isolated and repaired quickly by well-equipped staff, with no need for a boil water advisory. The same issue in a village may take longer to fix and may result in the need for a boil water advisory to be issued while repairs are arranged and completed.

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