The City of Sarnia delivers safe and clean drinking water to Sarnia residents through a system of watermains, known as the Municipal Drinking Water System.  The Safe Drinking Water Act and the regulations of the Ontario Ministry of the Environment, Conservation and Parks (MECP) require the City of Sarnia to provide safe drinking water to all of its residents, otherwise known as the Standard of Care. 

In order to keep the drinking water safe and protect public health, the City proactively works and plans to prevent contamination of the drinking water system from incidences of backflow. This plan includes creating a Backflow Prevention Program and passing a Backflow Prevention By-Law to enforce the program.

What is a cross connection?

A cross-connection is “any actual or potential connection between a potable water system and any source of pollution or contamination” (CSA, 2011).  cross-connection control, or Backflow Prevention, help to ensure our drinking water is protected.

How can contamination occur?

Back flow

Back flow is the reversal of the normal flow of water. Backflow can push or pull non-potable water inside the pipe from the customer‟s premises back into the municipal drinking water system. Backflow occurs when back pressure or backsiphonage conditions occur in a water line.


Backsiphonage can cause backflow if there is a drop in pressure or a negative pressure in the water line, such as a main break.

Back Pressure

Back Pressure can cause backflow when a source of pressure, such as a pump, creates a pressure greater than the one supplied by the municipal drinking water system..

The goal of this program

  • Inform and educate property owners on backflow prevention.
  • Identify properties that require a backflow prevention device where potential contamination of the municipal drinking water system may occur.
  • Maintain a database of certified backflow prevention device testers who are authorized to complete selection, installation and testing of devices.
  • Insure devices required under the by-law are being maintained and in good working order.
  •  Active compliance with the City of Sarnia, Backflow Prevention By-law.

Providing Sarnia residents with safe drinking water is OUR responsibility,  keeping it safe is EVERYONE’S.

Registered testers

All work required under the bylaw can only be done by a Registered Tester. For information on becoming a Registered Tester, please email

To learn more about Sarnia’s Backflow Prevention Program,
please contact:

Engineering Department
Public Works
651 Devine Street
Sarnia ON Canada N7T 1W9

More Information on ICI, Agricultural and Specific Residential (moderate or severe hazard) can be found here