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About Sewer Overflows


A sewer overflow occurs when wastewater is discharged into the environment – usually the nearest body of water – instead of being processed at a wastewater treatment plant. Sewer overflows include discharges from sanitary and combined sewers, as well as wastewater treatment plants. ​​

Access the real-time sewer overflow map​​



Sewer Overflows, Inflows, and InfiltrationSewer Overflows, Inflows, and Infiltration434894816

Why sewer overflows happen

The majority of the region's wastewater is processed at a wastewater treatment plant before it is released into the environment. Overflows can happen when heavy rainfall overloads the sewer system and also because of damage to pipes, power outages, or an equipment malfunction.

Sanitary and combined sewers

Sanitary sewers collect wastewater that is put down a toilet or drain – in homes and businesses – and carry it to wastewater treatment plants. Combined sewers carry both sanitary wastewater and stormwater in a single pipe. Combined sewers only still exist in older parts of Metro Vancouver and are designed to discharge into the environment during heavy rain, to avoid backups into homes and businesses. Overflows from combined and sanitary sewers that are caused by heavy rain are usually highly diluted by rainwater.

Wastewater treatment plant​ interruptions​

A wastewater treatment plant interruption means that wastewater has been released before the treatment process has been fully completed. This usually happens because of a po​wer interruption or equipment malfunction at the treatment plant.

Locations of sewer overflows​

Sanitary sewer overflows can occur anywhere in the region. Combined sewers exist only in the older parts of the region (Vancouver, Burnaby, New Westminster), so combined sewer overflows occur only in those areas. Sewer overflows occur in both municipal and regional sewer systems. ​

Monitoring and reporting sewer o​verflows

Metro Vancouver reports sanitary sewer overflows and wastewater treatment plant interruptions immediately to the federal and provincial governments, regional health authorities and associated municipalities. Combined sewers are monitored continually and overflows are reported annually to Environment Canada.

What is being done to reduce sewer overflows​

Metro Vancouver is working on a number of projects that will help reduce overflows. Metro Vancouver is upgrading aging infrastructure, building more wastewater storage tanks, installing back-up power in all pump stations, and increasing sewer capacity to accommodate growth.​

Metro Vancouver and member municipalities are also working to identify neighbourhoods where water seeps into pipes on private properties, which overloads sanitary sewers, and to replace combined sewers with separated sanitary and storm sewers. Separating these sewers is a long-term project that will likely take decades to complete.

What residents and businesses can do​

Damaged pipes and improperly connected roof and foundation drains on private property can let in rainwater and groundwater that doesn’t belong in our sanitary sewers. This is called in​flow and infiltration, and it increases flows in pipes which can cause sanitary sewer overflows.



Inflow and Infiltration, Inflow and InfiltrationInflow and Infiltration

A little inflow and infiltration from individual properties might not seem like a big deal, but when there are problems on many properties in the same neighbourhood, it can​ add up quickly to create serious challenges downstream. Proper maintenance of the pipes and drains on your property can help reduce inflow and infiltration, and prevent sewer backups and basement ​flooding. Homeowners and businesses should regularly inspect and maintain sanitary and stormwater pipes on their property.

 Related links



Environmental Management and Testing, Environmental Management and TestingEnvironmental Management and Testing
Real-time Sewer Overflow Map, Real-time Sewer Overflow MapReal-time Sewer Overflow Map
Stormwater and Drainage Management, Stormwater and Drainage ManagementStormwater and Drainage Management

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