Staying current with Canadian drinking water guidelines
Staying up to date with changes to Canadian Drinking Water Guidelines (CDWG) can be challenging for those involved in the assessment of drinking water quality and management of drinking water supplies. Since our last look at CDWG in 2019 there have been several new consultations and adopted changes to the guidelines, warranting a fresh look at what has changed over the past few years, what new guidance is available, and what consultations are currently under way.
How are drinking water guidelines developed?
Health Canada and the Federal-Provincial-Territorial Committee (FPTC) on Drinking Water establish draft guidelines for drinking water quality parameters (chemical, biological, and aesthetic) using current published scientific evidence. Draft guidelines go through a process of internal and external peer review, with scrutiny by the FPTC and consultation with scientific and technical audiences who focus on drinking water, and the public. This process can take several years and can result in confirmation or changes to existing guidelines, or introduction of new guidelines.
Drinking water guidelines are only established for contaminants that meet all three of the following criteria:
- Exposure could lead to an adverse human health effect;
- The contaminant is frequently detected, or expected to be detected in drinking water supplies throughout Canada;
- The concentration detected, or expected to be detected, in drinking water is of possible human health significance.
The guidelines usually set a Maximum Acceptable Concentration (MAC) in drinking water, which is based on scientific evidence of health effects and the likely route(s) and intensity of exposure (e.g., daily water intake). The MAC is set at a concentration that is protective of the most vulnerable persons (e.g., infants, children) and thus ensures protection of all Canadians.
Other criteria may also be established, such as an aesthetic objective (AO), based on ensuring that water is acceptable to consumers (e.g., colour, odour, or taste), or operational guidance values (OG) for parameters that could affect treatment processes or the water distribution system (e.g., aluminum). Health Canada also produces guidance documents for water quality parameters or issues that do not require a formal MAC, but may provide additional advice on operation, risk assessment, or treatment (e.g., corrosion control, quantitative microbial risk assessment).
How are drinking water guidelines updated?
CDWG are reviewed periodically to assess whether the scientific evidence on health effects, exposures, or treatment has changed. Changes to guidelines in other countries may also prompt a review of guidelines in Canada. The frequency of updates to CDWG for chemical parameters can depend on Health Canada’s review of chemical priorities in drinking water every four to five years, whereas new evidence on microbiological contaminants and operational factors are reviewed on an ongoing basis. The review process can result in the MAC being reaffirmed, increased, decreased, or guidelines being withdrawn. New parameters can also be added if the three criteria for establishing a guideline (above) are met.
What changes to CDWG have occurred since 2020?
There have been several updates to the Canadian Drinking Water Guidelines since 2020. Some of the key updates since 2020 are listed in Table 1:
Table 1 Changes to Canadian Drinking Water Guidelines since 2020
|Type of change||Year||Parameter||Current MAC|
|Reaffirmed MAC||2020||Total coliforms and E.coli||0 per 100 mL|
|2021||Metribuzin, herbicide||0.08 mg/L|
Dimethoate, organophosphate pesticide
0.02 mg/L (now additive with omethoate)
|Withdrawn guidelines||2020||Chloramines - withdrawn based on the low toxicity of monochloramine at the concentrations detected in Canadian drinking water|
|2022||13 pesticides and four other chemical substances – withdrawn as no longer likely to be detected in drinking water, (e.g. some pesticides no longer registered for use in Canada)|
|New guidelines||2021||1, 4-dioxane, synthetic chemical
Aluminum (in addition to existing OG)
|Increased MAC||2020||Barium, trace metal
Cadmium, trace metal
|2023||Malathion, insecticide and acaricide
Boron, trace metal
|Decreased MAC||2022||Dicamba, herbicide
In addition, to the changes in Table 1, several new guidance documents have been published for the following parameters:
- Use of Enterococci as an indicator in Canadian drinking water supplies (2020)
- Natural organic matter in drinking water (NOM) (2020)
- Overview of the microbiological aspects of drinking water quality (2021)
- Temperature aspects of drinking water (2021)
- Monitoring the biological stability of drinking water in distribution systems (2022)
- Waterborne pathogens (2022)
The full list of Canadian drinking water guidelines summarizes all current microbiological, chemical, physical, and radiological parameters, and provides an overview of changes. Provincial or territorial authorities will typically decide if and how CDWG are adopted into regional drinking water regulation. This can have implications for both large municipal water suppliers and small water systems, and those involved in oversight of these systems. Action may be needed where there is a new guideline or a decreased MAC (resulting in more stringent guidelines) to assess compliance and to identify ways to comply if found to exceed the new MAC. Health authorities may need to work with water suppliers to review historic monitoring data, if it has been previously collected, or collect new baseline data to identify supplies to communities, or certain populations that may be exposed to an exceedance of the MAC. Additional actions could include measures to protect source water from the contaminant, changes to water treatment approaches, future monitoring, provision of information on possible health effects to the public, and support to those on private water supplies who may need advice or support to test their water.
What’s coming next?
Recent consultations on CDWG concluding in 2023 have included a review of the MAC for antimony, draft operational guidance on sampling and mitigation for corrosion control to align with the changes to the MAC for lead in drinking water (2019), and proposed new objective of 30 ng/L for the sum of total per- and polyfluoroalkyl substances (PFAS). The results of the consultations will inform whether the guidelines are adopted as proposed, or if changes are required. Some additional chemical parameters for which guidelines or guidance are being developed or could be updated in the next few years are listed in Table 2.
Table 2 Parameters under review
|Parameter||Source of contaminant||Last published||Current guideline|
|acrylamide||Polyacrylamide used in water treatment, or in dam or well construction||None||N/A|
|arsenic||Natural and industrial sources||2006||MAC of 0.010 mg/L|
|asbestos||Decay of asbestos cement in water mains, or erosion of natural deposits||1989||No existing MAC due to insufficient evidence of health hazard from ingestion of water|
|atrazine||Herbicide||1993||MAC of 0.005 mg/L|
|haloacetic acids||Disinfection by-products||2008||MAC of 0.08 mg/L for total HAA|
|trihalomethanes||Disinfection by-products||2006 and 2009 addendum||MAC of 0.100 mg/L|
|iron||Heavy metal, usually naturally occurring||1978||No health based MAC An AO of < 0.3 mg/L is set based on colour, smell, taste|
Water system owners and operators, and public health practitioners involved in drinking water oversight or monitoring, can look for new consultations here, and can also subscribe to receive updates when new content is added to Health Canada’s Water Quality site. This can help practitioners find out as soon as a new consultation is launched or an updated guideline is published. Keeping up with this information can help public health to prepare for potential changes well in advance, and gather evidence on the communities that may be affected.
How can I find out more about drinking water contaminants?
For more information on Canadian Drinking Water guidelines, consultation documents, and drinking water contaminants (Water Talk Fact Sheets), check out Health Canada’s Water Quality – Reports and Publications and your relevant provincial and territorial agencies responsible for drinking water.
For more water-related resources from the NCCEH see our subject guides on:
- Small drinking water systems and private wells
- Drinking water guidelines and governance
- Recreational coastal, freshwater, and other untreated natural waters
- Cyanobacteria in Freshwater
- Lead in drinking water