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Viruses in Drinking Water

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Posted on October 22, 2019

Health Canada recently introduced a technical document to be used in conjunction with the Health Canada Virus-1Guidelines for Canadian Drinking Water Quality. This document outlines the various types of enteric viruses found in Canadian drinking water, how frequently they are found in water supplies, and the impact enteric viruses have on the health of Canadians. The findings of the report boil down to this: enteric viruses are present to some degree in all sources of Canadian drinking water. While the concentrations and regions in which they are found vary, their greater propensity to cause infection compared to other waterborne pathogens makes viruses a top priority. The new guidelines recommend a treatment objective of a 4-Log (99.99%) inactivation or removal of viruses. Canadians and water treatment providers should strive to meet this goal.

Monitoring water supplies for viruses and other pathogenic organisms is a complicated and costly process. This is why we typically rely on certain generally harmless indicator organisms, such as Total coliforms and E. coli , to provide insights into the possibility of pathogens, like enteric viruses, being present in drinking water. It is becoming clear, however, that these indicator tests alone are an imperfect tool to protect the public. Health Canada is now recommending a “source-to- tap approach”, which takes a more holistic view of all the risks that can contribute to viral contamination of drinking water. Although testing for indicators, at the source and tap, a minimum of two times a year is incredibly important, the results must be viewed with caution and used only as one input into a risk-based framework. Additionally, it is recommended to consider the location, construction, depth of the well when assessing contamination risk.

Surface waters, shallow wells, and ground waters thought to be under the influence of surface water are considered by Health Canada to be high risk sources for potential contamination. So, the treatment goal should be applied. For deeper, more secure water sources special consideration to geology must be given. Evidence to date indicates that fractured bedrock aquifers are more susceptible to viral contamination. Seventy ( 70%) of Canadian regional aquifers that provide drinking water are fractured bedrock.

Enteric viruses are fecal contaminants making onsite septic systems a significant risk. Studies have reported that 35%-78% of private wells with septic systems nearby have shown viral detection.

Reviewing water reports, well reports and maintenance history, septic age and maintenance history, should all be used in conjunction with annual microbial tests as a standardized way to determine risk of contamination. If these records aren’t available or are incomplete, the health- based target of 4 log (99.99%) removal or inactivation of viruses should be applied.

Removal or inactivation of viruses relies on specific water treatment technologies. In this technical document ultraviolet light (UV) is recognized as a technology fit to achieve the treatment objective. Health Canada confirms that a UV system certified to achieve a UV dose of 40mJ/cm² is effective in providing a 4 Log (99.99%) inactivation of viruses making it a perfect addition to any new or existing water treatment system.  For help understanding which UV system is best suited to your needs, speak to a water treatment professional or check out our Help Me Choose tool.

To read the full report, click  here.