Prioritization process for the development of Guidelines for Canadian Drinking Water Quality

Background

To help keep drinking water safe, Health Canada has a series of Guidelines for Canadian Drinking Water Quality. The guidelines recommend maximum levels for microbiological, chemical and radiological substances in drinking water. Drinking water containing substances at or below these maximum levels should not affect human health over a lifetime. Health Canada develops guidelines in close collaboration with the provinces, territories and other federal departments through the Federal-Provincial-Territorial Committee on Drinking Water.

Canadian drinking water supplies are generally of excellent quality. However, water in nature is never pure. It picks up bits and pieces of everything it contacts, including for example minerals, silt, vegetation, fertilizers, and agricultural run-off. While most of these substances are harmless, some may pose a health risk. To address this risk, Health Canada has a process to identify and prioritize which substances require new or updated guidelines.

This page describes how Health Canada prioritizes chemicals. It also describes how the department considers microbiological and radiological contaminants, as well as operational factors affecting drinking water.

Prioritization of chemicals

Health Canada identifies chemical priorities in drinking water every four to five years. There is some flexibility to add urgent priorities if needed. The process for prioritizing chemicals examines many sources of information, including the following:

  • updates in the scientific literature, risk assessment or treatment methodologies
  • new actions in other countries
  • input and data from the provinces, territories and other federal departments

The prioritization process has four steps: gathering data; screening the data; initial prioritization based on health risks; and final prioritization taking into consideration treatment and measurement capability and jurisdictional needs (Figure 1).

Figure 1: Overview of prioritization steps for chemical contaminants
Figure 1 - Text description

This process provides a science-based, methodologically-robust and transparent way to identify and prioritize chemicals/groups requiring the development of a drinking water risk assessment. The four key steps are 1) Data gathering, 2) Triage, 3) Draft health-based list and 4) establish priority groups. New information can be in putted into the process at any time.

Prioritization steps for chemical contaminants

Step 1 - Data gathering: Health Canada compiles an initial list of chemicals based on any the following:

  • chemicals with guidelines older than six years
  • chemicals with new scientific information or international reviews
  • input and requests from provinces, territories and other federal departments (e.g., water monitoring data, Canadian sales and use reports for pesticides, etc.)
  • updates to drinking water quality standards and guidelines in other countries or by international agencies, such as the World Health Organization

Step 2 - Screening: Chemicals on the initial list are screened to see if there is enough data to determine whether:

  • exposure to the chemical could cause adverse health effects
  • the chemical is likely to be found in Canadian drinking water at levels that could cause adverse health effects
  • the chemical is likely to be found frequently and in a large number of Canadian drinking water supplies

Step 3 - Initial prioritization: Chemicals with enough data are prioritized as high or low for development of guidelines or screening values based on health risks as a function of toxicity and exposure. High priorities are chemicals with (a) high toxicity and high exposure risk, (b) lower toxicity but high exposure risk or (c) high toxicity and low exposure risk. Chemicals without enough data are classified as "need more data". Low priorities are not considered further.

Step 4 - Final prioritization: The chemicals that were determined to be high risk to health or "needing more data" are sorted into four groups for priority assessment taking into consideration the ability to measure a chemical and remove it from drinking water, and federal, provincial and territorial (FPT) needs.

The priority assessment groups are as follows:

  1. chemicals that are classified high based on health risk, treatment and measurement methods, and FPT needs
  2. chemicals that are classified high based on health risk and either treatment and measurement methods or FPT needs
  3. chemicals that need more data to determine health risk, but are classified high based on treatment and measurement methods and FPT needs
  4. other chemicals that are lower health priority and not considered further until the next prioritization cycle
Figure 2: Relationship of priority assessment groups
Figure 2 - Text description

Figure 2 shows the classification of chemicals into priority rating groups, based on four criteria represented by circles. The orange circle represents the criterion "High risk to health", the dark green circle represents the criterion "Treatment and measurement methods", the light green circle represents the criterion "FPT needs", the light blue circle represents the criterion " More data is needed to assess health risks ”and the dark blue circle represents the criterion“ Low risk to health ”.

Chemicals are classified into four priority rating groups numbered 1 to 4:

  • Chemical substances classified in the “high priority” category according to the criteria “High risk to health”, “Treatment and measurement methods” and “FPT needs”, this being illustrated by the number 1 appearing in the center of the intersection of orange, light green and dark green circles.
  • Chemical substances classified in the “high priority” category according to the “High risk to health” criterion and either the “Treatment and measurement methods” criterion, or the “FPT needs” criterion, this being illustrated by the numbers 2 appearing in the center of the intersection of the orange and dark green circles and in the center of the intersection of the orange and light green circles.
  • Chemicals which require more data to determine the risk to health, but which are classified in the “high priority” category according to the criteria “Treatment and measurement methods” and “FPT needs”, this being illustrated by the number 3 appearing in the center of the intersection of the light blue, dark green and light green circles.
  • Chemicals whose health risk is "low" and which will not be taken into account before the next cycle of prioritization, this being illustrated by the number 4 appearing in the dark blue circle located at the right of the other circles.

Table 1 lists the chemicals in priority assessment groups 1 to 3, based on outcomes of the 2018-2019 prioritization process. Health Canada will publish proposed and final assessments on Canada.ca and a notice of publication in Canada Gazette, Part I.

Table 1 Priority assessment groups for new chemicals

Priority assessment group 1: Chemicals that are classified high based on health risk, treatment and measurement methods, and FPT needs

Bisphenol A
Chlorate/chlorite
Cyanide
Estriol/estrone
Fluoride
Formaldehyde

Glyphosate
Hydrocarbons
Nitrilotriacetic acid
Pentachlorophenol
Phthalates

Sodium
Styrene
Trichloroethylene
Vanadium
Zinc

Priority assessment group 2: chemicals that are classified high based on either health risk alone or on health risk and one or more of treatment, measurement methods or FPT needs

Alkylphenols
Bentazon
Benzene
Carbontetrachloride
Chlorine
Chlorobenzoquinones
Cobalt
Dichlorprop

EDTA
Ethalfluralin
Ethylene glycol
Flonicamid
Fluoxetine
Flupyradifurone
Fluxapyroxad

Metaldehyde
Molybdenum
Monochlorobenzene
Nickel
Silver
Thallium
Trichloroethane1, 1, 2-

Priority assessment group 3: chemicals that need more data to determine health risk, but are classified high based on treatment and measurement methods and FPT needs

17-Alpha-dihydroequilin
4-Nonylphenol dethoxylates

Creosote
Haloacetonitriles

Hydrogen peroxide
Lithium

Acronym: EDTA is ethylenediaminetetraacetic acid

Prioritization of microbiological and radiological contaminants

Health Canada considers microbiological and radiological contaminants separately from chemical ones. For microbiological contaminants, it reviews new and updated evidence on an ongoing basis rather than a cyclical one because these contaminants pose greater and more immediate health risks than chemical ones.

For radiological contaminants, Health Canada continuously monitors any scientific developments to determine if the guidelines need to be revisited. The current guideline values were developed based on the recommendations of the International Commission on Radiological Protection, an independent organization designed to advance the science of radiological protection to increase public protection. Table 2 lists prioritized microbiological and radiological contaminants.

Table 2: Prioritized microbiological and radiological contaminants

Microbiological, radiological & other priorities: parameters that are reviewed on an ongoing basis or that have impacts on treatment processes that may indirectly affect human health

Boil water advisories
Cyanobacterial toxins

Drinking water avoidance advisories
Legionella

Radiological

Prioritization of operational factors

Health Canada does ongoing reviews of new and updated information on operational factors affecting drinking water. Operational factors include parameters (e.g. natural organic matter, turbidity, pH and alkalinity) that can affect drinking water treatment processes, aesthetic properties of treated drinking water and/or conditions in the distribution system. Operational parameters can indirectly affect human health through their impact on drinking water treatment processes or through the potential generation of disinfection by-products. Table 3 lists operational factors being monitored.

Table 3: Prioritized operational parameters

Operational factors: parameters that are reviewed on an ongoing basis or that have impacts on treatment processes that may indirectly affect human health

Colour
Intake-to-tap
Operational

Odour
Premise plumbing

Taste
Withdrawal of select guidelines

More information

If you are interested in learning more about prioritizing contaminants for the development of Guidelines for Canadian Drinking Water Quality, please contact us at hc.water-eau.sc@canada.ca.

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