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COVID-19 wastewater surveillance dashboard

Technical notes

This page has information about how we conduct wastewater testing and the limitations of the data. It also includes definitions for some of the scientific terms used in this dashboard.

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Scientists across the country provide wastewater surveillance data through their provincial and territorial networks.

Scientists are still learning about how to detect and measure COVID-19 in wastewater. While there are different ways of doing this, the scientific community, including the Public Health Agency of Canada, is working together to build a standard that will help everyone understand, compare and share data about COVID-19 in wastewater.

We’ve compared wastewater data with local data and found that the trends are consistent. Differences in the strength of the wastewater signals are mostly due to differences in processing methods.

We present COVID-19 viral load as a 7-day rolling average because high levels on a single day don’t show the broader trend. Our approach helps us to understand the overall trends while giving you better information to make your own health decisions.

We present data for all sites, including where an areas is serviced by multiple wastewater treatment plants.


While wastewater surveillance offers many advantages, it does have some limitations.

The wastewater signal can be hidden by the composition of wastewater, which varies by community. For example, ground or surface water can make the COVID-19 wastewater signal stronger or weaker. This can be an issue during seasonal snow-melt and large rain events.

The wastewater signal can also be affected by:

We’re working with our partners to identify other issues with wastewater surveillance, and developing measures to reduce the effects.

Wastewater surveillance also detects people with or without symptoms. Considering the above limitations, we’re not sure how much virus is shed with each wave. For this reason we don’t recommend comparing wastewater surveillance data from different waves of COVID-19 to estimate the number of cases in a community.


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