FAQ - Backwater Valves

Simple graphic of a house in a valley with a manhole behind it partway up a hill

Backwater valves prevent sewage from backing up into structures, particularly when homes are located below the elevation of the next upstream sewer manhole. In general, when service lines are properly equipped with backwater valves, sewer line obstructions should result in overflow sewage making its way into manholes rather than into homes.

Though a standard backwater device will protect most homes from backups in the sewer main, there are exceptions. Homes with especially low service connections may require additional protection, such as a grinder pump with a more robust check valve. Two examples would be a basement sewer connection or a home with later additions that are lower than the original home sewer plumbing.

DPU is available to work with customers to determine whether their property is at risk and whether a backwater valve is advisable or required. In some cases, customers may need risk assessments from qualified plumbers or engineers.

Do I already have a backwater valve?

Are you unsure if your home has a backwater valve already? Backwater valves can be installed indoors or outdoors. If installed with indoor plumbing, they are usually found in a crawl space or basement in an accessible area. If installed outdoors, they are installed in the yard buried in line with the home’s sewer service line with a vault or PVC riser to allow access.

The maps linked below show properties that are below upstream sewer manholes, however DPU does not maintain information on where property owners have installed backwater valves.

Townsite property map(PDF, 19MB)

White Rock property map(PDF, 16MB)

What is the cost to install a backwater valve?

An indoor installation in a basement may cost $1000 to $1500 depending on the existing conditions. An outdoor installation requiring excavation may cost $2000 to $5000 depending on site conditions.

Who installs backwater valves?

A licensed plumber is qualified to install backwater valves.

Does a backwater valve require maintenance?

A backwater valve requires periodic maintenance to perform correctly. Depending on the manufacturer’s requirements the maintenance typically consists of removing and cleaning the check assembly. Failure to maintain could result in the check assembly not seating correctly allowing flow to leak back through the valve into the home.

What is the likelihood that I may experience an overflow if I do not have a backwater valve?

The DPU estimates that less than five homes per year experience backups into the home located below the upstream manhole due to not having a backwater valve.

If my home has a low pressure sewerage pump station, do I need a backwater valve?

Low pressure sewer systems are equipped with check valves that prevent flow from entering home plumbing, therefore a home with a low pressure sewer system does not need a separate backwater valve.