The Effect of Flooding on Private Drinking Water Systems


10 April 2018

Flooding and a private drinking water system

Every year as snow melts, the run-off (often called spring run-off) results in contaminants entering groundwater. In addition to spring runoff, Ontario often receives record amounts of rainfall, which can lead to flooding in many areas. Flooding combined with annual spring runoff can cause a higher-than-usual risk of contaminants, particularly in private well water.

It’s important to take flooding seriously, understand the risks and know what steps to take to protect you and your family.

What are the risks?

Flooding can affect water quality, and this is a particular concern for rural residents in Ontario on private drinking water systems. Be aware that flooding may cause contamination of private water sources, such as wells.

"Private drinking water systems serve many Ontarians, particularly in rural and remote areas. These systems are vulnerable to contamination with fecal pathogens, particularly during flooding, and should be tested frequently."

— Dr. Anna Majury, Clinical and Environmental Microbiologist, PHO

What should I do?

  • If you use a private well for your water supply, ensure that you reach out to your local public health unit or your local Public Health Ontario laboratory to have your water tested. Don’t drink, use the water in food preparation, or for brushing your teeth, until it has been determined that there are no indicators of bacterial contamination in the water source.
  • It is important to test frequently throughout the year. However, in times of flooding, heavy rainfall, snow melt or spring run-off, it is recommended that private well owners test more often (minimum of once per month).

Flooding and a private sewage system

If your property is at risk of a flood, or flooded, consider the effect on your private sewage system. A flooded sewage system will not function properly and can cause problems such as:

  • sewage backup in your home, and;
  • contamination of your water supply. 

In the event of a flood, contact your local public health unit for guidance regarding how to manage your private sewage system during the flood period.


If you have any questions, or would like to have your water tested, please reach out to your local public health unit.

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Updated 10 April 2018