From sewers to parks: Can wastewater save Europe’s hottest cities?

The Athens metropolitan area is home to a third of Greece’s population and attracts up to 10 million tourists per year. But its drinking water supply is under pressure.    

Athens’s drinking water comes from lakes up to 190 kilometres away. Extended droughts, intensified heat events and decreasing winter snow have lowered water levels dropping to 60% of their capacity.   

The Athens Water Supply and Sewerage Company (EYDAP) is investing €2.1 billion to protect Athens’s water supply in the years to come.  

In addition to campaigns promoting water conservation and improved irrigation, EYDAP is working with experts from the National Technical University of Athens and the EU research project IMPETUS on a decentralised ‘sewer mining’ unit.     

The sewer mining plant is connected directly to the municipal sewage system and locally filters and disinfects wastewater in stages. This produces high quality water for irrigation, recharging aquifers and for other uses like fire protection or cleaning. 

About 25 cubic meters of water per day is filtered and stored in a subsurface tank. The safety of the water is tested regularly by EYDAP.   

Katerina Dimitrou oversees new activities at EYDAP and says they want such units to irrigate every park in the wider Attica region. They want to use this model unit to convince both citizens and authorities that this method can reduce pressure on drinking water supplies. 

The prototype was built at a local park in Markopoulo, a town located 10 kilometres south of Athens Airport and home to around 22,000 people.  

Integrating the unit into the park and improving public acceptance of having a sewage system right in front of them is the role of Maria Petinaki. She’s an architect specialising in environmental design and ecological building techniques, and was invited to oversee the entire setup. 

The town’s mayor Konstantinos Allagiannis says sustainability and circularity were the main reasons to accept the sewer mining unit in the community park. “This unit is autonomous, because it has solar panels and it does not affect the environment at all because its construction is made of recyclable and natural materials,” he said. 

The unit uses sensors to monitor the system, sending data into the control room and then further on to a ‘digital twin’ at the National Technical University of Athens (NTUA). This digital twin covers the entire Attica region, receiving environmental data and turning it into a realistic 3D simulation.   

“Having a digital twin is important,” said Prof. Christos Makropoulos from the NTUA’s School of Civil Engineering and is part of the IMPETUS project. “We can understand in real time how the environment responds to pressures. It allows us to run long term scenarios of climatic pressures, plan for interventions and see how the two interact.” He says the technology can be easily expanded and transferred to other regions in Greece and Europe.  

Having already benefited from the prototype, the mayor of Markopoulo wants to use the plant in other green spaces, help irrigate local crops, and provide water for aquifers and firefighting. 

Athens’s sewer mining unit may be small, but its impact reaches beyond a single park. By reusing wastewater locally, the whole city is reducing pressure on distant reservoirs. Alongside the digital twin, this could be the solution to water resilience in a warming world.