New data from the city shows that billions of litres of water containing untreated sewage flowed into Winnipeg rivers in 2018.

The City of Winnipeg uses a combined sewer system, which collects rainwater, snowmelt and wastewater from homes and businesses, all in the same pipe. It then takes it to the treatment plan and then releases it into the river.

But when there’s heavy rainfall or snowmelts, the sewers are overloaded and the untreated content overflows into the river.

In 2018, 8.65 billion litres of combined sewage overflowed into the rivers, up from 6.6 billion litres in 2017. The data also shows that last year there were a total of 1,353 combined sewer overflows.

According to the city’s report, sewer overflow fluctuates from year to year, based on factors such as the amount, intensity, frequency, location and duration of rainfall, as well as river levels. 

Based on data from a heavy rainfall in 2015, the city estimates about 4 per cent of overflow is wastewater, while the other 96 per cent is rainfall runoff. 

That means of the 8.65 billion litres of sewage that discharged into rivers in 2018, they city says 346 million litres were wastewater and 8.3 billion litres were rainfall runoff. 

The city began tracking overflow volumes in 2013, with 2015 being the year with the largest discharge at nearly 12.5 billion litres.

The report notes that the city has been working to reduce sewage overflows for a number of years, but the work is expensive and lengthy.