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Providing the public with access to safe, clean water involves a complex series of protective measures and interventions. The government of Canada uses a combinatorial approach to this challenge, focusing on source water protection, adequate treatment, and distribution system integrity. Risk assessments and mathematical modelling are used by the government to create guidelines that prevent pathogens and other contaminants from reaching consumers. While this system has been generally effective, outbreaks still occur and oversights in these assessments may be leaving certain populations vulnerable to infection. Here we discuss the current regulations for water quality in Canada, and how cutting-edge research and technologies may improve them in the future.
In Canada, all levels of government contribute to keeping your water safe.
The federal government defines the Guidelines for Canadian Drinking Water Quality (GCDWQ), which set health-based targets for pathogen levels and other contaminants that are most likely to pose risks to public health. While these guidelines are not legally binding, they act as a framework for provinces and territories to establish their own legally-enforceable standards for water quality.
The provinces and territories enact their own water quality standards that adhere to the federal guidelines. These standards are tailored to each geographical location, which can come with unique challenges. They set enforceable standards, fund and manage infrastructure such as treatment plants and distribution systems, and act to protect source water from contamination.
Municipalities are typically responsible for operating and maintaining water treatment facilities, as well as conducting regular testing to make sure drinking water is safe according to both the federal and provincial regulations. They are also responsible for ensuring safe distribution of drinking water throughout the municipality.
The National Plumbing Code is the primary source of water quality regulations in Canada, providing guidelines for everything from drainage systems to the materials being used. All private plumbing installations must adhere to this code. These regulations are essential to ensure that the water being distributed remains safe for use.
Health Canada uses a set of standards known as the Quantitative Microbial Risk Assessment (QMRA) in drinking water when developing the GCDWQ. The QMRA uses mathematical modelling to estimate the potential health risks posed by a waterborne pathogen.
The QMRA considers the route of exposure to a particular pathogen, for example whether it is more likely found in prepared foods or your tap water. Then, it looks at how much of this pathogen will cause illness, compared to how much is likely to be ingested from the water supply. The result is a calculated risk level used to inform governing bodies on how to address pathogen levels in their regulations.
Compiled by the Upper Midwest Water Science Center, the following graph summarizes data used by the QMRA to quantify risk, showing how different pathogens cause illness at lower levels of exposure:
All enteric pathogens pose risks to human health and therefore should be included in risk assessments, however this approach is unfortunately unfeasible at this time. The QMRA instead includes several reference pathogens, which represent the behaviour and treatment response of several similar pathogens. Those included in the assessment are:
● Bacteria: E. coli O157:H7 and Campylobacter are used as reference bacteria. Both cause significant gastrointestinal illness and are prevalent in Canada. These bacteria are known to respond to water treatment similar to other bacteria pathogens, making them ideal references.
● Protozoa: Giardia and Cryptosporidium are the most common waterborne protozoan pathogens in Canada, with potential to cause widespread disease. Their behaviour is well-documented and they are a challenge to treat with conventional methods, making them good indicators of treatment effectiveness.
● Viruses: Rotavirus is currently used as a reference for enteric viruses, however no one enteric virus has been found to be truly representative. While rotavirus has some features of a good reference virus - common, causes disease, well-studied - it is not perfect. Prevalence and strain type can be geographically dependent, and young children are often more susceptible to infection, which is not considered by the QMRA.
While the QMRA model is thorough and has been adopted as standard practice internationally, it has some significant limitations.
For example, some methods used to identify waterborne pathogens are outdated. More accurate detection methods have led to surprising links between waterborne pathogens and public health, which would have previously gone unreported. As our understanding of the risks we face improves, this must be reflected in assessments such as the QMRA.
As mentioned above, an ideal reference virus has historically been difficult to identify. Enteric viruses can be particularly difficult to test for, difficult to treat, and can cause an infection from ingesting just a few particles. Proper representation of these viruses is required to accurately estimate the risks involved.
The QMRA also does not account for extreme weather events. Heavy rainfall and warmer temperatures can increase the levels of pathogens in source water, which is not considered in the model.
While the QMRA is largely effective for preventing disease in healthy populations, it does not consider demographic data in its model. Pregnant women, children, elderly people or those who are immunocompromised may be particularly vulnerable to some infections.
For these reasons, water scientists have been calling for the QMRA to keep up as technologies develop and pathogen levels change.
Canada's approach to regulating water quality depends on a combination of federal guidelines, provincial standards, and municipal implementation. The QMRA plays a crucial role in informing these regulations by estimating the risks posed by waterborne pathogens. While this system has been largely effective in ensuring safe drinking water for Canadians, it faces challenges such as outdated detection methods, difficulties in identifying ideal reference viruses, and limitations in considering vulnerable populations. As our understanding of waterborne pathogens evolves and new technologies emerge, there is a pressing need for the QMRA and related water quality regulations to adapt and improve, ensuring continued protection of public health in the face of changing environmental conditions and scientific advancements.
