Published on: 28.10.2019

Information produced by Finnish Environment Institute

Where does wastewater go in the sewers?

Vesi valuu viemäriputkesta.

What would life be like without underground sewers? Wastewaters would flow in open drains, and the stink would be revolting. Human health would be at risk, and natural environments would also suffer.

The building of sewers in Finnish cities began in Vyborg in the latter half of the 19th century, with other cities soon following suit. In Helsinki, this undertaking began around 1880.

In the beginning, sewers took wastewaters straight into the nearest water area. When it started becoming contaminated, the outlet was moved further away, until it was finally understood that wastewaters must be treated. Modern sewer networks always end at a wastewater treatment plant. While most municipalities have their own plants, some have also joined their forces.

Today’s sewer networks are large, such as the almost 5,000 kilometres of sewers in the Helsinki Metropolitan Area. Not all of them are for sewage, however, as some convey rainwater.

Sewers are designed to be built on a slope, letting gravity bring wastewaters to the treatment plant. If the plant is far away or over a hill, the wastewater must be pumped along. There are over 500 pumping stations of this kind in the Helsinki Metropolitan Area.

Disposing of inappropriate items or food waste, including cooking fat, in the sewer may cause blockages. Sewers often need to be cleaned out, and heavy rains can also cause them to flood.

Image: iStockphoto