Think of the valve as a movable gate on one relevant drain connection. In ordinary conditions it lets drainage move out. If flow reverses, the gate can close and help limit reverse sewer flow through that connection.
Normal flow: drainage moves away from the home
During normal drainage, the valve's movable part is open enough for flow to pass in its intended direction. The valve's precise construction and placement depend on the approved installation; the diagram is conceptual, not a specification.
Reverse flow: the flap can close
If sewage moves back toward the property, a suitable valve can close to help limit that reverse flow through the connection where it is installed. This is not a guarantee against basement flooding. It does not stop water entering through other routes, such as surface water, groundwater, foundation openings, roof drainage or plumbing leaks, and it does not protect unrelated connections.
A closed gate changes what can drain
The same closure that helps limit reverse flow can also prevent wastewater from connected fixtures from draining out while the valve remains closed. Toilets, sinks, showers, laundry and other connected plumbing may not be usable normally. Avoid normal water use until conditions are safe and the valve has been assessed or cleared in accordance with the manufacturer's instructions and qualified guidance.
Maintenance follows the installed device
Follow the manufacturer’s instructions and keep the access point reachable. Ottawa recommends periodic maintenance or a check before forecast heavy rainfall, including attention to debris, function, caps and covers. These are general reminders, not a procedure for opening or servicing every valve.
For safe homeowner checks, warning signs, and when to call a plumber, see the dedicated Ottawa backwater valve maintenance guide. Also read the City’s basement-flooding prevention guidance.
Know the boundary of the protection
The valve only concerns reverse flow through the relevant sewer connection. It is one part of plumbing protection, not a promise that a basement will stay dry or that every sewer-related risk is eliminated. Identify the connection and overall drainage context with a qualified professional before choosing a project.
Bring the right questions to the assessment.
Use the homepage planning tools to organize what you know; those tools run in your browser. The separate assessment form attempts to email your inquiry to listerplumbing@hotmail.com only after you consent and submit. An inquiry is not a confirmed appointment.