Viemärit

Viemärit, or sewers, are the underground networks that collect wastewater and, in many areas, stormwater, and transport it to treatment plants or discharge points. They form an essential part of municipal water and sanitation infrastructure and are typically owned and operated by city or regional utilities.

Sewer systems can be categorized as combined sewers, which carry both sewage and stormwater, or separate systems where wastewater and stormwater are conveyed in different networks. The network consists of pipes, manholes, pumping or pressure stations, and sometimes retention basins or overflow structures to manage peak flows. Materials commonly used include concrete, clay, ductile iron, or PVC.

Historically, urban sewer networks expanded in the late 19th and early 20th centuries as cities grew, with ongoing modernization through the 20th century. In many countries, including Finland, municipal authorities manage sewers as public utilities and coordinate with wastewater treatment plants.

Maintenance includes inspections (often with CCTV), cleaning, root control, and repair and rehabilitation of pipes, plus measures to reduce infiltration and inflow to minimize sewer overflows. New techniques such as relining and pipe bursting extend the life of older networks.

Viemärit protect public health and water bodies by removing waste and stormwater before discharge, supporting compliance with environmental regulations such as the EU Water Framework Directive. Challenges include aging infrastructure, infiltration and inflow, frost damage, root intrusion, and climate-related flood peaks, while governance remains municipal or regional and subject to national environmental oversight.