Beneath the streets of Prague stretches an infrastructure longer than the journey to Madrid and back—the city's water supply network measures almost 4,600 km, while its sewer system extends for nearly 5,000 km. The true pulse of the metropolis therefore beats several metres below ground, where pipelines, utility tunnels and sewers intersect, serving more than 1.4 million residents every day, as well as thousands more beyond the city’s boundaries. Some sections of the sewer network have been operating continuously for over a century. Today, the metropolis is therefore planned not only in terms of its layout, but also in terms of its cross-section: the capacity of sewers, pressure zones, and the performance of treatment plants determine where new neighborhoods can emerge, how dense the development will be, and where tram lines or parks can be built. This hidden layer is not a technical detail, but a fundamental condition for the city's growth.
Lindley's plan: A sewer system ahead of its time
By the end of the 19th century, Prague’s sewer network ranked among the most advanced in Europe. The concept of a unified system was designed by British engineer William Heerlein Lindley, who gave the city a logical backbone of sewers that carried water by gravity to a central treatment plant. The system was built with extraordinary precision: with sufficient gradients, inspection entrances, and robust profiles that ensured its long service life. The main trunk sewers, designated by letters, sewer A and later sewer B, played a key role, gradually connecting the individual parts of the rapidly growing city.
The oldest and architecturally most valuable trunk sewer, sewer A, was built from double-fired glazed bricks. It carries wastewater from Prague 1, 2 and 3, and part of Prague 5.
Sewer A begins in the junction chamber of the so-called Foreigners' Entrance beneath the Old Town Hall and runs along Pařížská Street under Čechův Bridge towards Bubeneč, where it empties into the Central Wastewater Treatment Plant. This section, which is more than three kilometers long, drains water from the historic city center and other parts of the wider center. The system also included a foreigners' entrance as a control and security access point to the underground system, used for maintenance and protection of the infrastructure. Even then, it was a technically and organizationally well-thought-out project that responded to the hygiene crisis of the 19th century and rapid population growth. Some of the main sewers are still in use today, but their capacity is currently struggling to meet the new demands of a growing metropolis.
“While what lies beneath the ground may sometimes mean torn-up streets, it is absolutely essential for the everyday life of Prague’s residents,”
says Deputy Mayor for Infrastructure Michal Hroza.
The foreigners’ entrance under the Old Town Hall is a junction chamber where sewer A begins.
A sewer that will unlock entire neighborhoods
Debates about urban development often take place above ground, but the real limitations lie beneath it. Without modernizing the networks, it is impossible to expand development or plan new neighborhoods. That is why many projects do not begin with an architectural study, but with a calculation of sewer capacity.
A symbolic project for the future is the new trunk sewer B. It will follow the historic route from the late 19th century, which still carries wastewater from Žižkov, Karlín, Holešovice, and part of Letná to the Central Wastewater Treatment Plant. However, its capacity is no longer sufficient for the planned development of the northern inner city. The new sewer, approximately two kilometers long, will therefore run from the Karlín and Libeň areas towards Bubny and on to connect to the existing backbone system. This will create a new high-capacity underground connection that will relieve the historic pipeline and enable the safe drainage of sewage and rainwater from the transforming areas. The construction, costing approximately CZK1.1 billion, is to be built between 2028–2030, with project preparation running from 2026–2027. Its significance lies not in its length, but in its impact: it is key to the transformation of the largest development area in the metropolis, Bubny-Zátory. Its catchment area could see an increase of up to 110,000 residents and jobs in the coming decades. It is an infrastructure project without which the development of the new district could not begin at all. In other words, without the sewer, there would be no neighbourhood.
“Technical infrastructure sometimes determines what a city looks like on the surface,”
says architect and Deputy Mayor Petr Hlaváček.
The new two-kilometer sewer B will create an underground connection between Karlín, Libeň, and Bubny-Zátory, thus relieving the historic route leading to the sewage treatment plant in Bubeneč.
Where the rain goes
One of the least visible but most important processes in the city is water management. The sewer system must be able to cope with normal operation as well as extreme rainfall, which is becoming more frequent due to climate change. Prague has seven main trunk sewers and over 128,000 sewer connections. More than 90% of wastewater goes to the Central Wastewater Treatment Plant in Bubeneč, the largest water management facility in the city. This centralization is no coincidence; a large treatment plant can purify water more efficiently and consistently than a network of smaller facilities.
However, water is no longer treated solely as waste. Engineers are increasingly looking at its energy potential. Wastewater maintains a stable temperature that can be harnessed through heat exchangers to warm buildings or heat domestic water. Similar systems are already operating in major European cities, and Prague is examining their use in new neighbourhoods and public buildings. The sewer network is thus gradually evolving from purely sanitary infrastructure into a discreet yet steady source of energy.
The Bubeneč treatment plant is a key point in the entire underground network. It is the place where sewers from most of the city converge and from where the treated water returns to the river.
Investments you can't see
This is precisely why investment in technical infrastructure is increasing. It determines whether the city can grow from within and do so sustainably. “Over the past three years, the volume of investments in the renewal of water management infrastructure in Prague has doubled and is approaching five billion crowns. These are projects that will not turn into iconic buildings or tourist attractions, but without them, no iconic building could be created,” says Deputy Mayor for Infrastructure Michal Hroza, adding: “Even technical facilities are gaining a public dimension today. An example is the Vinohrady Waterworks complex, which is currently being transformed into the Hydropolis center. Visitors can learn about the journey of water through the city, climb to the observation deck in the tower, and enter a space that combines technology, education, and public space.” Infrastructure is thus shifting from an invisible background system to becoming part of the city’s cultural landscape.
The Hydropolis project in the former Vinohrady Waterworks will present water as a key urban resource, from its journey through pipes to the modern technologies that enable its reuse.
Beneath the streets of Prague, there is a parallel structure governed by the laws of physics that keeps the metropolis running every second of every day. Its capacity and technical parameters already determine where construction will take place and what Prague will look like in ten, twenty, and even fifty years. The importance of these hidden structures, which are a prerequisite for quality urban planning, was discussed at CAMP as part of the series Prague’s Big Changes.
You can view the recording here:
