On June 14, 2023, Oxford County Council endorsed Oxford County By-law No. 6544-2023 Cross Connection and Backflow Prevention to further safeguard the municipal drinking water system by preventing contamination from non-drinking water sources. Backflow events can significantly impact residents, businesses, and the environment by impacting water quality, posing a health risk to consumers, and causing service interruptions.

General Info

About Backflow 

Backflow is a reversal of the normal flow of water. It occurs under "back pressure" or "back siphonage" conditions, which push or pull water from inside a private-service connection back into the municipal drinking water system.


Back pressure illustration Back siphonage illustration

Backflow risk occurs at a cross-connection

Backflow events can impact the water quality in the distribution system and at neighbouring properties if the water “backflows” through a cross connection. A cross-connection is any connection between the municipal drinking water system and any source of contamination.

backflow prevention graphic showing water going from a water tower into the ground and into a home

Backflow Prevention Devices (BPD)

A BPD isolates the water supply of private services in order to prevent the reversal of the water flow. 

Premise isolation BPD must be installed at or near the water meter prior to plumbing junctions to ensure private side plumbing is isolated from the municipal water supply. Additionally, any water provided to customers or employees must be fully isolated from hazardous fixtures within the premise.
Types of acceptable BPDs 

Reduced Pressure Principal Assembly (RP)

Photo of an RP valve

  • Two independently acting check valves separated by a reduced pressure zone
  • Installed between two shut-off valves
  • Each check valve is fitted with test cocks for annual testing
  • Used for health hazards and severely hazardous connections (i.e. hospitals, medical/dental facilities, industrial or chemical plants)

Double Check Valve Assembly (DCVA)

Photo of Double Check Valve Assembly (DCVA)


  • Two internally loaded check valves, force-loaded or internally weighted
  • If one check valve fails to close, the other will prevent backflow
  • Each check valve is fitted with test cocks for annual testing
  • Can be used for all non-health hazard connections (i.e., fire sprinklers, irrigation systems)

Pressure Vacuum Breaker (PVB)

 Photo of Pressure Vaccum Breaker (PVB)


  • Independently acting check valve, force-loaded to a closed position and an independently operating air inlet valve force-loaded to an open position and located downstream of the check valve
  • Installed between two shut-off valves
  • Fitted with two test cocks for annual testing 
  • Can ONLY be used for non-health hazard (no chemical additives), automatic sprinkler systems

Who is impacted by the by-law?

The Backflow Prevention By-law applies to moderate or severe hazard industrial, commercial, institutional properties, as well as select multi-residential properties, based on their classification under the CSA B64 series standards. 

Oxford County's responsibilities 
  • Administer the backflow prevention program for premise isolation through Backflow Solutions Inc. (BSI).
  • Maintain records of cross-connection survey reports and BPD test reports.
  • Register authorized testers in accordance with the by-law.
  • Ensure property owners meet the by-law requirements.
  • Address questions or concerns and provide information updates.
Property owner's responsibilities 
  • Contact a certified plumber registered with Oxford County (see the list on this page).
  • Schedule a cross-connection survey.
  • Install and/or register an approved BPD if required.
  • Complete and affix a backflow prevention test tag to the device or immediately adjacent to the device. You can purchase test tags online or call Customer Service at 519-539-9800 to discuss in-person or telephone purchases.
  • Complete an annual inspection of the backflow device.

Qualified contractors

An individual approved by Oxford County to conduct backflow prevention installation, testing, and maintenance. Contractors must be certified by the Ontario Water Works Association or other governing body and qualified to conduct work in accordance with the by-law. 

Contractor's responsibilities 
  • Take a backflow certification course.
  • Contact Oxford County to register as a certified tester.
  • Perform initial cross-connection surveys with fees payable to Oxford County via phone or in person at the Oxford County Administration Building
  • Perform annual backflow device inspections with fees payable to BSI
  • Purchase Backflow Device Test Tags 
  • Submit inspection forms to Oxford County.


Program Administration 

Oxford County has retained an external service provider (BSI) to administer the Backflow Prevention Program (BPP) cross connection control surveys and BPD reports. 

  • Contact BSI to register as a qualified contractor
  • Submit BPD test reports (link coming soon - Nov 27)
  • Submit cross-connection survey reports (link coming soon - Nov 27) 
  • Only backflow device testers registered with the County will be able to submit cross connection control surveys and annual backflow prevention device test reports.
  • BSI Customer Service Information: 
    - Phone: 604-492-0613
    - Email: backflow@bsionline.ca
    - Website: https://bsionline.ca


Qualified Contractor list for Cross Connection Control Surveys 

Oxford County strongly recommends obtaining multiple quotes and does not endorse or provide recommendations of services or prices.


Approved list of qualified contractors 


Qualified Contractor list for Backflow Prevention Device Tests  

Oxford County strongly recommends obtaining multiple quotes and does not endorse or provide recommendations of services or prices.


Approved list of qualified contractors 


Administrative fees

Property owners                Current fees
Cross Connection Survey Submission Fee  $30 + HST
Backflow Test Report Submission Fee  $35/test
Test tag (good for 5 years) $25/device
* In addition to the above noted Oxford County administrative fees, customers will also incur other direct costs to purchase any required BPD(s) and/or employ a qualified backflow tester for the purposes of BPD installation, inspection, testing, repair(s), etc.  

Frequently Asked Questions


What is a cross-connection?

Any actual or potential connection between the municipal drinking water system (watermain) and any pipe, vessel, tank, plumbing fixture, equipment or device through which it is possible for used, polluted or contaminated water or any other substance to enter the municipal drinking water system.


What is an example of a cross-connection?

A common example is a garden hose connected to a hose bibb at one end and the other end of the hose lying in a pool, puddle or any other source of non-potable water. Another example would be the makeup water for a hot water heating boiler. The water in these systems can be rusty and oily and may pose a health threat if consumed.


Other common cross-connections found in plumbing and water systems include:

  • A water softener drain or other types of water conditioning equipment directly connected to a sanitary sewer
  • A chemical sprayer attached to a hose without a backflow preventer
  • A high-pressure washer utilizing soaps or cleaners connected to a hose bib or other sources of water without a backflow preventer
  • A lawn irrigation system installed without an approved type of backflow preventer
  • Using a hose to unplug blocked toilets and sewers
  • Photo developing equipment
  • An auxiliary water supply connected to the watermain
  • A toilet that does not have an anti-siphon float valve installed


What is backflow?

Backflow is a reversal of the normal direction of flow. Backflow may occur due to either back siphonage or back pressure.


What is back-siphonage?

Back-siphonage is a reduction in pressure in the municipal drinking water system (watermain) below atmospheric pressure. This can cause water to be pulled from the private-service side into the watermain. Some examples that may cause a drop in pressure are a watermain break, watermain flushing, or the use of a fire hydrant.


What is back pressure?

Back pressure is an increase in pressure on the private-service connection side above the pressure of the watermain. Some examples of issues that can cause this increase in pressure include malfunctioning booster pumps, improperly protected water heaters or water hammers.


What causes backflow?

An example is when there is a watermain break, and the area must be isolated and repaired. When the valves around the repair site are closed, the flow of water is stopped to all points of use, such as homes and businesses and begins to flow backwards towards the repair. This is back siphonage, and if there are cross connections, contaminants can be drawn into the municipal drinking water system.


What happens after backflow occurs?

When the repair is complete; and the regular pressure is restored, everything starts to flow in the proper direction. Any contaminants that may enter the water supply will flow toward any point of use (plumbing fixtures) in homes or businesses. The degree of hazard to health will be dependent on the type and amount of contaminant, the amount of time the situation goes unnoticed and whether or not a protective device is in place.


Why do water purveyors (suppliers) need to control cross-connections and protect their public water systems against backflow?

Backflow into the municipal drinking water system can pollute or contaminate the water in that system. The hazard created by backflow is generally identified in three groups: severe or high, moderate and minor. A severe hazard is likely to result in serious injury or death, while a minor hazard may affect the colour, odour and/or taste of the water with little or no health effects. Each water purveyor has a responsibility to provide water that is usable and safe to drink under all foreseeable circumstances. Further, the expectation of the public is that water quality supplied by the water purveyor is potable and safe to use, and it will remain so regardless of its use. For these reasons, each water purveyor must take reasonable precautions to protect its municipal drinking water system against backflow.


What is premise isolation? 

Backflow protection on the private-service connection directly after the water meter and before any cross-connections.


What is area protection?

Backflow protection is provided for a section of a piping system with potable and non-potable connections (that may or may not be considered cross-connections) downstream of a backflow preventer.


What is fixture protection?

Backflow prevention is provided at the connection to a fixture or appliance. Examples include built-in air gap on industrial dishwashers, lab faucet vacuum breakers, etc.


What is a "moderate" or "severe" hazard?

Moderate hazard: any minor hazard connection with a low probability of becoming a severe hazard.

Severe hazard: any cross-connection involving substances considered dangerous to health 


What is a backflow prevention device (BPD)?

A device that, when exposed to backflow conditions, closes the water loop, restricting the movement of water and preventing flow from the private-service connection into the municipal drinking water system.

Where are BPDs required to be installed as per the by-law?

  • Multi-unit residential (except those within the scope of Part 9 of the Ontario Building Code)
  • Industrial, commercial, and institutional buildings
  • Installed at entrances to buildings for new sprinkler services and on private-side connections of the water meter for domestic sprinkler services

Why do BPDs have to be tested periodically?

Mechanical backflow preventers have internal seats, springs and moving parts that are subject to fouling, wear or fatigue. These mechanical devices and air gaps can also be bypassed. Therefore, some backflow preventers have to be tested periodically to ensure  they are functioning properly, and others, such as an air gap, require a visual check to ensure  they are still in place. The testable backflow preventers must be tested by a Qualified Person.


Who is responsible for testing a BPD?

The owner of the property or agent of the owner (i.e., property manager), or as otherwise identified in the lease agreement.


What are the consequences for failing to comply with the testing or installation requirements?

Failure to comply with the requirements of the By-law may result in the disconnection of the water supply to the property.


Why did the County enact this by-law?

The by-law is consistent with the County’s Drinking Water Quality Management System, which is in place to provide safe drinking water to residents and businesses.


How do I become a Qualified Person for the purposes of carrying out tests and inspections?

You will have to register, complete, and pass the Cross Connection Control course. You must then provide your certification to the County to register as a Qualified Person and be included on the roster of Qualified Persons. When required to recertify, you must register, complete, and pass the recertification course and provide proof of recertification to the County.