Stormwater

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Stormwater refers to rainwater, snow melt, and drainage water from the foundations of buildings. Stormwater is generated in the built environment as a result of rain or melting snow.

Stormwater flows along the ground surface, roofs of buildings and other surfaces. From the ground, stormwater is usually conducted into stormwater sewers or open ditches, through which it eventually ends up in the sea or water bodies. Stormwater must not be conducted into a wastewater sewer. 

Various stormwater structures, such as stormwater sewers and open ditches, are needed to avoid any detriment caused by stormwater. Safe conducting and treatment of stormwater also requires planning of stormwater management as a whole. We take care of the planning and implementation of stormwater management in cooperation with the member municipalities, i.e. Helsinki, Espoo, Vantaa, and Kauniainen.

Stormwater management responsibilities

In the area of the Helsinki Region Environmental Services Authority, the duties and responsibilities of stormwater management are divided as follows:

  • Cities are responsible for stormwater management as a whole within their territory. For example, the city prepares a stormwater management plan and takes care of stormwater management in public areas, such as water removal from streets and flood routes. In addition , cities are responsible for the construction and maintenance of the municipality’s stormwater system. The municipality’s stormwater system includes, for example, open ditches and detention structures.
  • HSY is responsible for the construction and maintenance of the main stormwater sewer network in the separately defined stormwater sewerage area.
  • The owner or occupier of the property is responsible for the drainage of the building and the management of stormwater generated on the property. Stormwater can be absorbed and detained as well as conducted into HSY’s stormwater sewer or the municipality’s stormwater system in a controlled manner. The property must be connected to HSY’s stormwater sewer if it is located in the stormwater sewerage area.

Stormwater sewerage

HSY is responsible for stormwater sewerage in the Helsinki metropolitan area. We provide stormwater sewerage services in the stormwater sewerage area approved by our member municipalities. Our duties include the construction and maintenance of the main stormwater sewer network.

It is the responsibility of the owner or occupier of the property to build and maintain a lot sewer for stormwater from their lot to HSY’s main stormwater sewer.

Properties located in HSY’s stormwater sewerage area must be connected to HSY’s stormwater sewer network. You can apply for an exemption from the obligation to connect from your municipality’s environmental protection authority if the stormwater generated on the lot is, for example, absorbed on the lot or conducted into an open ditch.

As a rule, stormwater conducted into the stormwater sewer network is not treated, but rather discharged into water bodies as such. Stormwater must not be conducted into the wastewater sewer network.

Stormwater sewerage fees

We charge connection fees and basic rates for stormwater sewerage. The connection fee is determined as based on the property’s floor area and purpose of use. You can familiarise yourself with matters related to the property’s floor area in the water services price list.

  • The connection fee is charged when the property is connected to the stormwater sewer network.
  • All properties located in the stormwater sewerage area are subject to the basic rate for stormwater.

We use the fees charged for stormwater sewerage to cover the costs of stormwater sewerage. Costs are incurred, for example, from the construction of stormwater networks as well as the maintenance and servicing of the stormwater network.

Stormwater sewerage area

Billing criteria for the basic rate for stormwater

We charge a basic rate for stormwater from all properties in the stormwater sewerage area, as the stormwater sewer network serves all properties in the area. The basic rate must therefore also be paid for properties located in the stormwater sewerage area that are not connected to the stormwater sewer network or that have been exempted from connecting to the stormwater sewer network.

For instance, during heavy rains, stormwater may be discharged from properties into the stormwater sewer network even if at other times the property’s stormwater would be absorbed or conducted e.g. into an open ditch.

The basic rate for stormwater is invoiced in connection with a normal water bill.