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Leaky sewers cause hidden nutrient pollution in German urban waters

March 26, 2021
Sewers under Berlin, Germany. Image: SnaPsi | Flickr Creative Commons

A growing body of research suggests that untreated wastewater leaking from damaged or badly designed sewer systems is a key source of urban water pollution. However, data on sewer leaks and pollution is often missing from large-scale environmental assessments of urban areas.

A new study by Dr. Hong Hanh Nguyen and Dr. Markus Venohr from the Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB) in Berlin responds to this deficit. The authors propose the first German national estimation of wastewater losses from defective sewer systems by bringing calculations of sewer leaks into urban catchment models.

“Sewer systems are hidden in the ground and perform an important – but often unrecognised – job to collect wastewater ahead of its subsequent treatment,” says co-author Dr. Markus Venohr. “Damage to sewer systems, and any potential leaks into surrounding ground, are often hard to detect and quantify,” Dr. Venohr explains. “As a result, these aspects are usually neglected in large-scale nutrient emission modelling.”

The researchers upscaled local calculations of sewer leaks to both pipe, city and municipality scales using a combination of datasets and expert knowledge. They found that pollution from sewer leaks is found across both public and private sewers, but is particularly common in ageing pipes more than 40 years old.

“In our new paper, we calculate the contribution of losses from leaking sewer systems to overall Germany-wide nutrient emissions,” Dr. Venohr continues. “We discuss these nutrient losses within the framework of the LAWA-funded project AGRUM-DE, to which our work makes an important contribution.”

“Our study shows that sewer age and type, together with human population density, are key factors influencing the potential for sewer losses from public and private sewers,” says Dr. Venohr.

One key finding from the study is that water pollution from leaking sewers might account for between 10–20% more nutrient loads entering groundwater from urban areas across Germany than previously calculated.

“Overall, sewer leaks were estimated to locally add a substantial share of nutrient emissions from urban systems to groundwater, and thus to surface waters,” Dr. Venohr outlines.

The study stresses the importance of addressing leaky sewer systems as a potentially significant source of water pollution in urban environments. The authors suggest that their study framework will allow environment managers to better target pollution sources and incorporate leaky sewers as part of the long-term nutrient water management of agricultural and urban emissions.


Nguyen, H.H., Venohr, M. Harmonized assessment of nutrient pollution from urban systems including losses from sewer exfiltration: a case study in Germany. Environ Sci Pollut Res (2021).

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