Where does water come from?

This is the route of the water

The water flowing from your tap comes from the Kokemäenjoki river. From the river, the water is pumped into the pre-treatment plant of Turun Seudun Vesi Oy, where all solid matter, such as clay, is removed from the water. This process also removes 99% of all pathogens. The murky river water is transformed, and as it leaves the plant, it is clear. From there, it starts a 30-kilometre trip towards the Virttaankangas ridge.

The Virttaankangas ridge is partially located in a fracture in the deep bedrock. It was created at the early stages of the last glacial period as the ice sheet melted over 10,000 years ago. At its deepest, the several kilometres long fracture in the bedrock, filled by sand and gravel, reaches 100 metres below the surface.

The pre-treated water from Kokemäenjoki ends up in the ridge through a total of 19 recharge basins, whose combined surface area is 2.4 hectares. The water flows within the ridge for an average of three months. The soil in Virttaankangas not only cleans the water, but also optimises the pH value and hardness of the water in a completely natural manner. The next time that the water absorbed into the soil sees the light of day is when you open your tap. 

The water flows through the ridge like groundwater, and it is pumped up using groundwater wells, which only need to be drilled down approximately 40 metres, not until the bottom of the fracture in the bedrock. The location of the wells is more essential: two wells may be located only 70 metres apart, but one may produce three times the water the other one does, because of its location. The best wells can produce 12–13 million litres of water every day.

From the wells, the water is pumped into a filtered water reservoir, from where it starts its journey towards Turku after three months inside the ridge. The water flows the entire 60 kilometres to the Turku region using gravity. Virttaankangas produces over 62 million litres of artificial groundwater every day, which is enough to provide 300,000 people with domestic water. All of the water flows to the Turku region through pipelines every day.

In Turku, the water is directed to the Saramäki bedrock reservoir, where two caves, 235 and 250 metres long, are reserved for the water. Together, these two caves can store enough water to provide all of Turku, Raisio, and Naantali’s domestic water for one day. The water is chlorinated in the reservoirs to ensure its high quality through the pipe network. The remains of the chlorine are evaporated from drinking water if the water is stored in a pitcher for a while.

From Saramäki, the water flows to the water pipe network through Halinen. The amount of water in the network is automatically guided based on consumption, and the situation is constantly monitored in the control room. The water flows from Halinen in pipes up to 900 mm in diameter towards homes and water towers. The size of the pipes is decreased in the various areas of the network according to the need for water in the area.

The water towers have two significant tasks in the network: storing water for usage peaks, and maintaining suitable pressure. There are four towers in Turku: in Yliopistonmäki, Luolavuori, Parolanpuisto, and Juhannuskukkula, of which the latter is the largest. The size of the reservoirs in the towers varies between 9,000 and 12,500  cubic metres.

The monumental Yliopistonmäki water tower was designed by architects Erik Bryggman and Albert Richardtson. It was completed in 1941, and is now protected by the Finnish Heritage Agency. Today, the water tower facilities are also used for other purposes: the Yliopistonmäki tower, for example, hosts a climbing hall.

The water pipe network has an average 5 bar pressure, which ensures that the water flows at a suitable speed. Including the water for industrial uses, approximately 220 litres of water per resident is used in Turku every day. During the past decades, water consumption has decreased so that the network built in the 1970s and 80s is now rather oversized, even though the amount of people living in the area has increased. The large size of the pipes allows renovation of some sites by placing a smaller pipe inside the older one, without needing to dig open the entire route. 

Turku has a total of 818 kilometres of water pipes, and the network is renovated every year according to plan. Maintenance of the network is important, because a hole as thick as a pencil will cause 33,000 cubic metres of water to be lost per year. One way of noticing hidden leaks, which would otherwise be difficult to find, is using a Logger inspection. 

As water pipes can be broken and leak for many reasons, such as ground frost or corrosion, unexpected repair needs are also part of the everyday operations. In such situations, ensuring normal water management operations as soon as possible is important, and any leaks are reported to the residents of the affected area online. Unexpected water management breaks usually only last for some hours, causing only a short period of inconvenience to the residents. Cutting off water flow and limiting the affected area is taken care of using stop valves located in the streets.

The oldest pipes in the network date as far back as the early 20th century. However, age is not always an indicator of the condition of the pipes: cast iron pipes installed in the 1930s may be in mint condition, whereas many cast iron pipes from the 1970s require urgent renovation. Turun Vesihuolto is responsible for the trunk line pipes of the water network, but the property pipes and their condition is always the responsibility of the properties.

When water has been used, it flows down the drain. The amount of wastewater is estimated to be the same as the used domestic water. Wastewater is collected through the wastewater sewage system to the pumping stations using gravity, from where it is led towards the Kakolanmäki treatment plant. There are a total of 88 wastewater pumping stations in Turku, and a total of 599 kilometres of wastewater sewer pipes.

When water flows into the drain at your home, it passes through the wastewater sewers, ending up in Kakola at the Turun seudun puhdistamo Oy treatment plant, where a total of 90,000 cubic metres of wastewater from Turku and 13 other municipalities in the region is processed every day. 

When wastewater arrives at the intake pumping station, it is immediately pumped 20 metres upwards, from where it flows through the treatment process and all the way to the sea with gravity. Initially, any movables, such as items flushed down the toilet by accident or intentionally, is screened from the wastewater. Common findings include hygiene products, jewellery, and children’s toys, but even a bathrobe has been brought in by the wastewater.

Once any larger solid matter, sand, and grease have been separated from the water, it is directed into the primary clarification basin, where any fine solid matter descends onto the bottom of the basin and is collected as sewage sludge. The sludge is used at Topinoja to produce biogas for the use of cars and soil conditioner for green construction and agricultural uses, for example.

The core of the treatment plant consists of biological treatment, which means a basin full of tireless microbes and bacteria. The task of these microscopic organisms is to remove any phosphorus, organic matter, and nitrogen from the wastewater, which means that they are responsible for the main part of the overall treatment process. In order to maximise the cleaning effect, the conditions for the microbes and bacteria must be exactly right, which requires plenty of expertise. Therefore, the conditions are constantly monitored, and the condition of the bacteria and microbes is inspected using a microscope every month.

In the secondary clarification phase, the microbes which have done their job are separated from the cleaned wastewater, and the water is led into sand filtration basins. The filtration also ensures the quality and hygiene level of the processed water even during high flow rates. 

Before the treated wastewater is led away from the plant, Turun Seudun Energiatuotanto Oy collects heat from the wastewater. Including the heat collection, the wastewater treatment process produces 10 times more energy than it consumes. The energy collected in connection with the treatment process can be used to produce almost the entire district cooling in the Turku region as well as district heating for 15,000 households.

The entire treatment process of wastewater takes a maximum of two days. The cleaned water leaves Kakolanmäki through outlet pipes, runs towards the harbour, and flows into the harbour basin. After the introduction of the treatment plant, the phosphorus load in the Turku sea area has decreased by 72%.

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In addition to domestic and wastewater, the term rainwater is used to refer to both rainwater and the water resulting from snow and ice melting. Rainwater is led to a separate rainwater sewer, and the City of Turku is responsible for its processing. Less than 50 kilometres of mixed sewers, or sewers where both wastewater and rainwater is led, remains in use in Turku. In addition to sewer systems, other means, such as building wetlands, free flow channels, and green roofs, are used to manage rainwater. The aim is to consider rainwater management in all construction planning in the future.