Drinking water advisories

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In 2015, 78% of boil water advisoriesFootnote [1] in Canada were issued on a precautionary basis due to problems with drinking water equipment or processes. By contrast, boil water advisories issued due to the detection of Escherichia coli (E. coli) in drinking water samples accounted for 5%. Boil water advisories related to other microbiological water quality parameters, such as the detection of total coliform bacteria or unacceptable turbidity levels, accounted for 17% of total boil water advisories.

Causes of boil water advisories, Canada, 2010 to 2015

Stacked column chart
Long description

The stacked column chart shows the proportion of causes of boil water advisories in Canada (Water quality - E. coli; Water quality - Other microbiological parameters; and Equipment and process) for 2010 to 2015. Most boil water advisories issued in Canada between 2010 and 2015 were issued on a precautionary basis due to problems with drinking water equipment or processes.

Data for this chart
Causes of boil water advisories, Canada, 2010 to 2015
Cause of boil water advisory 2010
(percentage of boil water advisories)
2011
(percentage of boil water advisories)
2012
(percentage of boil water advisories)
2013
(percentage of boil water advisories)
2014
(percentage of boil water advisories)
2015
(percentage of boil water advisories)
E. coli 8 5 5 7 5 5
Other microbiological parameters 28 18 18 17 14 17
Equipment and process 64 77 77 76 81 78

Download data file (Excel/CSV; 1.40 KB)

Note: Data used in this indicator come from a variety of agencies and jurisdictions across Canada and represent a subset of the Canadian population. National use of the Canadian Network for Public Health Intelligence Drinking Water Advisories application has not yet been reached and national totals are not available. See this indicator's Data Sources and Methods document for more detail. The Water quality - Other microbiological parameters category includes detection of total coliform bacteria, high turbidity levels, and/or exceedances of maximum acceptable concentrations or drinking water standards in drinking water systems.
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, meaning they are typically issued before drinking water quality problems happen, and can take three forms: Do not consume, Do not use and Boil water.

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 disease-causing micro-organisms, such as bacteria, viruses or parasites, could be in the drinking water. "Do not consume" and "Do not use" advisoriesFootnote [1] are typically used when a chemical contaminant is suspected or confirmed in a drinking water supply. Both of these types of advisories are rare, representing approximately 2% of all drinking water advisories in Canada annually.

Most boil water advisories are issued because the equipment and processes used to treat, store or distribute drinking water break down, require maintenance, or have been affected by environmental conditions. This broad array of reasons includes issues such as broken water mains, planned system maintenance, power failures or equipment problems. In some 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 E. coli signals the possible presence of other disease-causing microbes, including bacteria, viruses or parasites. 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. Some strains of E. coli can cause stomach illness in humans along with other, more serious health problems. 

The category Water quality - Other microbiological parameters identifies advisories issued due to changing conditions inside the drinking water system that typically do not represent a health risk to consumers. Under this category are 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 2015, 79% of boil water advisories were issued for drinking water systems serving 500 people or less. This pattern is consistent with that observed from 2010 to 2014.

Boil water advisories by community size, Canada, 2010 to 2015

Stacked column chart
Long description

The stacked column chart shows the proportion of boil water advisories by community size (0-100 people; 101-500 people; 501-5000 people; and Over 5000 people) from 2010 to 2015. Systems serving 500 people or less received 80%, 78%, 76%, 79%, 82% and 79% of boil water advisories in 2010, 2011, 2012, 2013, 2014, and 2015, respectively.

Data for this chart
Boil water advisories by community size, Canada, 2010 to 2015
Community size 2010
(percentage of boil water advisories)
2011
(percentage of boil water advisories)
2012
(percentage of boil water advisories)
2013
(percentage of boil water advisories)
2014
(percentage of boil water advisories)
2015
(percentage of boil water advisories)
0-100 people 48 42 42 41 43 44
101-500 people 32 36 34 37 39 35
501-5000 people 19 21 21 20 17 18
Over 5000 people 1 2 2 2 1 3

Download data file (Excel/CSV; 1.17 KB)

Note: Data used in this indicator come from a variety of agencies and jurisdictions across Canada and represent a subset of the Canadian population. National use of the Canadian Network for Public Health Intelligence Drinking Water Advisories application has not yet been reached and national totals are not available. See this indicator's Data Sources and Methods document for more detail.
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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