Updated guidelines for drinking water quality
By Dianne Saxe and Jackie Campbell
By Dianne Saxe and Jackie Campbell
March 3, 2011 – In late December, Health Canada released its Guidelines
for Canadian Drinking Water Quality, prepared by the
federal-provincial-territorial Committee on Drinking Water. The new
guidelines supersede the 1996 edition, as well as more recent updates
with respect to different contaminants or parameters.
March 3, 2011 – In late December, Health Canada released its Guidelines for Canadian Drinking Water Quality, prepared by the federal-provincial-territorial Committee on Drinking Water. The new guidelines supersede the 1996 edition, as well as more recent updates with respect to different contaminants or parameters.
While only the summary document is available online, this provides an excellent overview of developments in drinking water protection over the past 15 years, and acts as a helpful review to remind us how changes to the guidelines are made.
Below, we briefly review the updated guidelines and discuss the process (and documents) used to establish guidelines on a formal and informal basis.
Highlights of the 2010 Guideline
The 2010 summary highlights some parameters for which guidelines have been issued or revised since the 1996 edition. For example, acceptable turbidity values are now provided according to the type of filtration system used (as opposed to a single figure used in the earlier guideline).
More stringent maximum acceptable concentrations (MAC) have been introduced for some parameters, including arsenic, uranium and some radioactive isotopes. The MAC for trichloroethylene, a solvent used mainly in metal degreasing operations and enters our water supply through industrial effluents, was lowered by a factor of 10 in 2005, based on extensive scientific review of risk of cancer and adverse reproductive effects3. As well, where no guideline values existed in 1996 for some parameters, these are now in place, for example, for antimony, bromate, chlorate, chlorite, haloacetic acids.
Following a systematic review of older guidelines, the updated guideline reaffirms the current guidelines for more than 40 parameters (for example, several chemicals, taste and temperature) and archives older guidelines for parameters that are no longer found in our drinking water at concentrations of concern to human health (for example, certain pesticides that are no longer used in Canada).
The lingo: guidelines, technical documents, guidance documents
The CDW establishes formal guidelines only for contaminants that meet three criteria, namely where
• exposure to the contaminant could adversely affect health
• the contaminant is likely found in a "large number" of drinking water supplies across the country
• it is or could be expected to be detected at a level that is possibly significant to health.
Where a contaminant does not meet all three criteria, the CDW may elect not to set a formal numerical guideline or develop the Guideline Technical Document (GTD), which sets out supporting scientific and technical documentation for each parameter.
However, the CDW may develop a Guidance Document for contaminants or specific issues that do not meet these criteria, and has done so in several instances. Such documents provide operational or management guidance relating to specific issues (for example, issuing boil water advisories, controlling corrosion in distribution systems) or set out risk assessment information (for example, potassium that enters our water supply from water softeners). These documents are intended to be used by drinking water authorities for information about contaminants, and to provide guidance in case of spills or other emergencies. The process for Guidance Documents includes public consultations, as is the case for GTDs.
How are guidelines established?
Consultation documents are first published on Health Canada's website for public comment. At the time of writing, the only current consultation posted is a proposed GTD for certain enteric protozoa Giardia and Cryptosporidium, which are transmitted via feces and may cause severe diarrhea and dehydration, among other symptoms. The document provides a comprehensive review of the health risks associated with exposure to these pathogens, evaluates recent studies and suggests approaches to reducing concentrations of these pathogens in drinking water, and acceptable level of risk. Following a review of comments received during consultation, the CDW will establish a Drinking Water Guideline for these parameters, if required.
Several GTDs that should soon be posted for public comment are listed in the guideline summary. These include ammonia (which currently has no numerical guidelines), as well as other parameters for which MACs were established as far back as 1986, and require review: carbon tetrachloride, chromium, fluoride, turbidity and vinyl chloride.
These health-based guidelines have been developed for several chemicals (including by-products of disinfection), micro-organisms and physical substances found in Canadian drinking water supplies. As well, the guidelines consider aesthetic effects (taste, odour and colour) and treatment processes/technologies (water turbidity can interfere with chlorination, while pipe corrosion affects drinking water infrastructure).
Provinces and territories may adopt some or all of these guidelines, either as guidance documents or by regulation as enforceable drinking water standards. In Ontario, for example, the drinking water quality standard for arsenic is 0.025 mg/L. In 2007, the province noted that it would review this standard, citing the more stringent Health Canada guidelines, which had in 2006 adopted a standard of 0.01 mg/L 9. Ontario's arsenic standard did not change. On the other hand, Nova Scotia adopted the federal guidelines (as these are amended from time to time) as binding standards in 2000.