Backflow prevention

What is a Backflow Preventer and How Does it Work?

In this plumbing blog post, we discuss backflow preventers and how they work. We are here for all your plumbing and renovation needs.

What is a backflow preventer and how does it work?

A backflow preventer is a device plumbers install on your home's water pipe to prevent contamination. The water should only flow one way, and that is in your home. This device stops water from flowing in the opposite direction back into the main water supply, and that is why we are here; to help keep your drinking water clean and untouched. As residents of Ontario, we are fortunate to have such systems in place to keep our families safe from any potential contaminants in the water.

For example, backflow can happen when there’s a break in the main water line or when a fire hydrant is opened for use. Because pressure is lost during these events, water is no longer being pushed forward into your home and will flow backwards into the city water lines. When this happens, backflow can contaminate the public drinking supply with:

Fertilizers/pesticides
Human waste
Chlorine from pools/spas
Soap from sinks/dishwashers/showers
And that’s where a backflow prevention system comes in handy. Let’s take a closer look at how a backflow prevention system works. See Diagram of backflow prevention HERE.

What does a typical cross-connection look like?
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 could 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 a municipal supply
A toilet that does not have an anti-siphon float valve installed
Who is responsible for establishing and administering a cross-connection control program?


It is important to note that the responsibility for establishing and administering a cross-connection control program is with the individual municipality or water purveyor (authorities). For this reason, there may be differences between the types of cross-connection programs that different authorities may have implemented. For more information on individual programs, you should check with your respective municipality or supplier of water. See more related to this subject HERE.

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