The Sewer Network is a system of underground pipelines that carry domestic, industrial and pretreated waste water to wastewater treatment plants. It is a critical part of urban life, helping to prevent pollution of water and the natural environment as well as maintaining public health.

The World Bank and the Global Water Security & Sanitation Partnership (GWSP) are supporting governments to develop and implement sewer networks that meet modern expectations. This includes ensuring that the design of new networks is robust and capable of delivering on their intended lifespan – 50 to 100 years, depending on climate conditions – while also meeting the growing need for improved sanitation service delivery in cities.

Sewers are designed to carry wastewater under pressure through a variety of conditions, including varying amounts of infiltration, sewage flow and the presence of biofilms. These complex interactions can have negative impacts on the environment as well as on people’s health and wellbeing.

A typical sewer line can contain many different types of structures, including manholes, inlets, culverts and pipes. These can vary in size and shape from one another and can be located in any direction within the pipeline, making it difficult to identify a sewer line from a map or other reference point.

There are also other factors that affect the location of a sewer line in the ground, such as infiltration and exfiltration. Infiltration can reduce the capacity of The Sewer Network because it can enter the pipes at points where joints and cracks may exist in the pipe, while exfiltration can result in the sewer system leaving the ground, which can cause contamination.

As a result, it is important to understand what each component of the sewer network brings to the overall design.

Combined Sewer Overflows

As in most Slovak cities, a combined sewer network is used in Trnava to mix rainwater and sewage water. Often, this water is discharged directly into the sea or river without treatment, which can have a negative impact on the environment. This problem can be addressed through the use of swirl concentrators, which create a vortex that separates impurities in water to concentrate them in a much smaller volume and allow them to be treated before being released.

Similarly, a separate sewer network can be used in some cities to transport sewage from domestic and pretreated industrial sources, or in areas that are not suitable for a combined system. These systems are usually built with temporary storage areas to treat runoff before it is released into the sewers, reducing the potential for harmful effects on the environment.

Misuse of the sewer network can cause blockages which can restrict the flow of sewage, impacting on the health and welfare of citizens. It can also contribute to environmental and societal impacts, as well as being costly to address.

A strong network needs a comprehensive approach that includes a range of stakeholders, including households. This means working with them to understand what they need from their sewer network, what can be done with the existing infrastructure and what is possible in non-conventional ways, such as providing flexible solutions. Such approaches can help to maximize connections and connect more people, especially those who are traditionally excluded from accessing services.