Water management networks
The total length of the water supply and sewerage network in the Helsinki Metropolitan Area is about 7,600 km.
Water supply network
The overall length of the water supply network in the Helsinki Metropolitan Area is about 2,900 km. Of this, about 300 km are water mains that convey water to water towers and large consumption centres. The water distribution pipes branch off of the mains, and the properties are connected to the distribution pipes through their own water service pipes.
Some of the most important water mains connections in Helsinki have been ensured by means of water pipes installed in rock tunnels. In the tunnels, the condition of the pipes can be regularly monitored and the pipes are protected from frost heave and other similar stresses. The tunnels are situated at a depth of 30–80 metres, so they do not hinder the normal activities of the community or the later use of the land.
In order to ensure the distribution of water, the water supply network has been built in the shape of a circle. The network is equipped with shut-off valves to ensure that water supply interruptions caused by pipe breakage are limited to the smallest possible area.
The water distribution system is monitored by means of a remote monitoring system. The water towers and booster stations as well as the most important valve grids are within the remote control system.
HSY regularly monitors water quality in the distribution network by taking water samples from different sampling sites around the network. In addition to HSY’s process laboratory, water quality is monitored by the health protection authorities of each individual city.
The total length of the sewer network in the Metropolitan Area is about 4,700 kilometres, of which about 2,700 kilometres are wastewater and combined sewers and about 2,000 kilometres are storm sewers. There are also 60 kilometres of sewers that have been excavated into the rock.
Two sewerage systems are used in the Helsinki Metropolitan Area. Outside Helsinki city centre and in Espoo, Vantaa and Kauniainen, there is a separate sewerage system where only wastewater is conveyed through the sewers to the Viikinmäki wastewater treatment plant and stormwater is led directly to the nearest water body. Most of Helsinki city centre belongs to an area served by a combined sewerage system where both stormwater and wastewater are conveyed to the Viikinmäki treatment plant through the same sewer. The combined sewerage system represents about 6 per cent of the total length of the sewers.
The wastewater sewerage system is designed, as much as possible, in such a way that the wastewater flows to the wastewater treatment plant by gravity. However, due to the relief of the terrain, this is not always possible and wastewater pumping stations are needed.
Some 450 wastewater pumping stations are used in the Helsinki Metropolitan Area. The stations are monitored and controlled by means of a remote monitoring system.