Out with the Old, In with the New – Canada’s Updated CDWQG

Posted on October 19, 2022

Last month, the Canadian Drinking Water Quality Guidelines (CDWQG) were updated to reflect current scientific knowledge surrounding drinking water in Canada.  In this revision, some guidelines have changed, and some parameters have been removed; either way it’s important to stay up to date on these changes and revise your testing programs accordingly.  As your Big Picture Sidekicks, we have summarized these changes below and encourage you to review the official tables, here.

In with the NEW!

All the NEW parameters fall into the Chemical and Physical category and are used primarily as herbicides. The guidelines for these parameters are health based, based on aesthetic considerations, or established based on operational considerations.  The great news here is that CARO can test for all these newly listed parameters via our environmental labs in Alberta and BC, so we have you covered!

1. Bromoxynil

This organic compound is a nitrile-based herbicide.  The common route of entry into drinking water sources is through leaching and/or runoff from agricultural use.  This new parameter carries a Maximum Acceptable Concentration (MAC) that is based on health impacts.

2. Dicamba

The common source of this parameter in water is from groundwater leaching or runoff from agricultural or other uses. Similar to Bromoxynil, the MAC is based on heath impacts.

3. Dichlorophenoxy Acetic Acid (2,4-D)

The common source of this parameter in water arises as a result of its high potential to leach into groundwater and/or run off from agricultural and non-cropland use.

4. Dimethoate and Omethoate

Omethoate is a metabolite of Dimethoate, so it is not surprising that these two herbicides are introduced into the regulations together.  The common source of this parameter in water is leaching and/or runoff from agricultural use. The MAC in this case is specifically assigned to Dimethoate as the parent compound, but the intention here is that the sum of both species does not exceed the MAC for Dimethoate.

5. Diquat

The common source of this parameter in water is from leaching and/or runoff from agricultural use, and it can be added directly to water to control aquatic weeds.  Leaching into groundwater is unlikely. The MAC is based on health impacts.

6. 2-Methyl-4- Chlorophenoxyace Tic Acid (MCPA)

This one’s a mouthful to say, so it is often referred to by its acronym “MCPA”.  As is the theme here today, the common source of this parameter in water is from leaching and/or runoff from agricultural and other uses.  MCPA is also a herbicide, used to control broadleaf weeds.

Wait, There’s More!

In addition to these new parameters, Health Canada has also released two new Guidance Documents, to provide advice on how to manage issues related to drinking water quality that may not necessarily be addressed through specific numerical guidelines:

The Guidance on Waterborne Pathogens provides a detailed discussion around the role of pathogenic microorganisms in drinking water quality and safety.  While CARO does offer analytical methods for many of the organisms mentioned (including our recently added Legionella testing), this document is also a great compilation of technical information and may be interesting to anyone with a passion for water quality!

The Guidance on Monitoring the Biological Stability of Drinking Water in Distribution Systems is a comprehensive guide on how to monitor the quality and health of your distribution system.   If you are working with this document to set up your own monitoring program, please note that CARO offers test methods for many of the parameters this guide recommends you keep your eye on.  Please reach out at any time for more information on how we can help!

And out with the OLD!

We’ll keep things nice and simple here!  In the table below (courtesy of Health Canada, in collaboration with the Federal-Provincial-Territorial Committee on Drinking Water), you will find a list of parameters that have been determined by Health Canada, in collaboration with the Federal-Provincial-Territorial Committee on Drinking Water, to no longer be found in Canadian drinking water supplies at levels that could pose a risk to human health.   Many of these compounds are herbicides/pesticides that are no longer registered for use in Canada, or groupings of parameters that now carry guidelines individually.

As always, CARO’s environmental labs in Alberta and BC are here to help if you’re setting up a monitoring program for your distribution system, or simply want to test the quality of the water you’re drinking.  If you want to learn more about CARO’s water testing capabilities head to our website here or get in touch with our team of charismatic scientists directly by emailing [email protected].