Stockholm's Water Pollution Solution: A Natural Approach

Stockholm, Sweden's capital, is renowned for its clean water and environmental sustainability initiatives. However, the city's water systems have faced challenges due to urbanisation, climate change, and pollution from settlements, industry, and traffic. Stockholm's water supply primarily comes from Lake Mälaren, which also faces the risk of saltwater contamination due to rising sea levels. To address these issues, Stockholm has implemented various measures, including improving wastewater treatment and reducing pollution levels in central bays. The city has also received recognition for its environmental efforts, such as the ISO Certification of Quality for its drinking water in 2017. Additionally, Stockholm was named the first European Green Capital in 2010 and continues to prioritise sustainability in its operations and policies.

Stockholm's water supply is sourced from Lake Mälaren, Lovö and Norsborg

Stockholm's water supply is sourced from Lake Mälaren, with the help of the waterworks at Lovö and Norsborg. The latter is one of the largest waterworks in the Nordic countries and has been supplying drinking water to Stockholm since the early 20th century. The Lovö waterworks supplies water to the northern and western districts of Stockholm, while the Norsborg waterworks delivers water to the central and southern parts of the city. Together, these waterworks provide clean drinking water to over a million people every day.

Lake Mälaren is a freshwater lake and the main regional source of drinking water. About 2 million people currently rely on the lake for water, and this number is expected to increase as Stockholm's population is projected to grow to 3 million by 2040. The water from the lake is purified at plants in Bromma, Henriksdal, and Loudden, which together filter around 400,000 cubic metres of sewage per day, including pollutants like nitrogen and phosphorus, before discharging it into the Baltic Sea.

Stockholm Vatten, a water and wastewater management company, is responsible for delivering drinking water to Stockholm and the surrounding areas. The company takes a holistic approach to its operations and aims to create the necessary conditions for the adequate delivery of water and an improved waste environment. It also owns and operates the tap water and sewage mains networks, pumping stations, and water reservoirs in Stockholm and Huddinge.

While Stockholm currently faces challenges in maintaining access to clean drinking water due to the impacts of climate change and urbanisation, the city has made significant progress in reducing water pollution. In the modern era, the city's water supply is sourced from Lake Mälaren and purified at plants, ensuring that residents have access to clean drinking water and can even swim in the central parts of Stockholm, which was not possible in the past due to high levels of pollution.

The city's water undergoes purification at three plants, removing pollutants like nitrogen and phosphorus

Stockholm is one of the cleanest capitals in the world. However, this wasn't always the case. In the 1940s, Riddarfjärden was extremely polluted and was called the 'sewage ditch'. Today, it is possible to swim in the central parts of Stockholm, and the city is taking steps to reduce water pollution.

The city's water undergoes purification at three plants—Bromma, Henriksdal, and Loudden—which together filter around 400,000 m³ of sewage per day, removing pollutants like nitrogen and phosphorus, before discharging the water into the Baltic Sea. The purification process typically involves two stages. In the initial stage, water is decontaminated using mechanical and chemical methods. This is followed by passing the water through slow sand filters that extract any remaining organic pollutants.

The city's drinking water is sourced from Lake Mälaren, Lovö, and Norsborg. This water supply serves about 2 million people and is expected to increase as Stockholm's population grows. The lake's water level is currently about 0.7 meters above sea level, but as sea levels rise, the difference is diminishing, leaving less room for extracting drinking water.

Stockholm is also facing challenges due to climate change and urbanisation. Increased rainfall, warmer temperatures, and fertiliser runoff from farms contribute to brownification and increased algae blooms in the water. Additionally, urban development can remove trees and vegetation that would otherwise stabilise the earth in sensitive areas, impacting water quality.

Stockholm's sewer system and industrial pollution negatively impact the city's lakes and watercourses

Stockholm's sewer system and industrial pollution have had a detrimental impact on the city's lakes and watercourses. The city's sewer system redirects surface water from smaller lakes to Lake Mälaren or Lake Saltsjön, reducing their catchment areas. This diversion of water flow has led to the disappearance of several historical lakes and the shrinking of others.

Additionally, the city's industrial activities contribute to water pollution, with high levels of metals and organic compounds detected in the central bays and surrounding waters. Stockholm's wastewater treatment plants, Bromma and Henriksdal, treat 355,000 m³ of wastewater daily from residents and industries. Despite the treatment process, which removes organic substances, phosphates, and nitrogen, the discharge of treated water into the Baltic Sea still impacts the environment.

Furthermore, the city's industrial history has left a legacy of pollution. Studies have shown that waterborne metal pollution, particularly lead, from pre-industrial mining and metallurgy, has contaminated lake sediments in the region. The impact of this historical pollution is greater than that of modern industrial activities.

The lakes and watercourses in Stockholm have also been affected by agricultural runoff, urban development, and climate change. Warmer temperatures and increased fertiliser use contribute to "brownification" and algae blooms, placing greater demands on water processing plants. Urbanisation, with more surfaces covered in tarmac or concrete, reduces the land's ability to absorb water, leading to increased drainage into waterways and a higher risk of flooding.

To mitigate these negative impacts, Stockholm Vatten och Avfall is working to reduce the presence of organic substances, phosphates, and nitrogen in the water. They also aim to minimise rubbish and environmental toxins by improving treatment processes and preventing toxins and trash from entering the wastewater.

Stockholm's water was historically contaminated with cholera and other diseases

Stockholm's water sources were historically contaminated with cholera and other diseases. In the 1940s, the city's harbour, Riddarfjärden, was extremely polluted and earned the nickname "the sewage ditch". The latrine and waste systems were managed by private entrepreneurs and were in very poor condition. Drinking water was not filtered, and the city suffered from cholera outbreaks in 1834 and 1853, which collectively resulted in about 6,000 deaths. The 1853 outbreak, which killed about 3,000 people, was likely influenced by poor hygiene and the lack of a centralised waste management system.

Following the 1853 cholera outbreak, Stockholm took steps to improve its hygiene and sanitation infrastructure. In 1859, the city inaugurated a central system for managing latrines and waste, which led to a significant improvement in hygiene conditions. Two years later, in 1861, Stockholm established its first waterworks for filtering and cleansing drinking water, resulting in a decrease in cholera-related deaths. Despite these measures, cholera outbreaks continued to occur in Stockholm almost every year until 1894, though none reached the severity of the 1834 and 1853 epidemics.

Today, Stockholm is one of the cleanest capitals in the world, and swimming is now possible in the city centre. The city has made sustainability and climate action a priority, with a well-developed district heating network that has helped reduce air pollution. Stockholm has also committed to investing in and accelerating climate and sustainability initiatives through the Swedish climate contract, which it signed in 2020.

Climate change could impact water quality, with heavy rainfall increasing sewage overflow

Stockholm, one of the cleanest capitals in the world, has made significant progress in reducing water pollution. In the 1940s, Riddarfjärden was extremely polluted and dubbed the 'sewage ditch'. Today, it has been transformed, and people can even swim in the central parts of the city. This success is largely due to the development of a district heating network, which has led to a major reduction in air pollution. Additionally, Stockholm has reduced its climate impact and greenhouse gas emissions by more than half since 1990, despite experiencing significant population growth during this period.

However, Stockholm still faces challenges, particularly regarding drinking water quality and access due to the impacts of climate change and urbanization. Lake Mälaren, the main regional source of drinking water, is vulnerable to saltwater contamination from rising sea levels. The water level of Mälaren is currently regulated to stay above sea level, but with sea levels rising, there is a risk that saltwater from the Baltic Sea will flood into the lake if no countermeasures are taken. This could permanently compromise the freshwater source for the growing population of Stockholm.

Climate change is predicted to bring about increased yearly rainfall, warmer and drier summers, shorter and wetter winters, and more frequent freezing-thawing cycles in Stockholm. These changes will have a significant impact on water quality and access. Heavy rainfall and intense storms can cause flooding, which not only affects water infrastructure but also leads to the overflow of sewage systems. When the pipes cannot cope, combined sewer overflow pipes allow wastewater to enter local rivers and seas. This discharge is untreated, releasing waste from toilets and sinks into the water bodies.

As Stockholm continues to expand with new housing, businesses, and industries, the risk of sewage spills during rainfall events becomes more frequent. This is because more houses are linking into existing sewage networks, reducing their capacity over time. The combination of increased rainfall and reduced capacity in the sewage networks results in more frequent pollution of rivers and water bodies by untreated wastewater. This issue is not unique to Stockholm but is a concern for many towns and cities.

To address this challenge, it is crucial to invest in and upgrade sewage networks to make them more resilient to climate change. Implementing separate wastewater and surface water systems, known as Sustainable Urban Drainage Systems (SuDS), can help capture and slow down the flow of water from roads and roofs into rivers. While new developments are required to have these separate systems, retrofitting existing combined sewage networks is also necessary to prevent rainfall from entering the sewage systems and contributing to overflow issues.

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