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The largest water treatment plant in the canton of Geneva

The Aïre STEP (‘STation d’EPuration’ or water treatment plant) is the main water treatment plant for the canton of Geneva and one of the largest in Switzerland. It receives wastewater from the city of Geneva, 24 towns in the canton and part of the cross-border region. More than 400,000 inhabitants are linked to the network. The wastewater is treated in permanence to protect the quality of the river Rhone where the treated water ends up.


Extensively rebuilt between1998 and 2003, the Aïre STEP replaced a plant dating back to 1967. It was redesigned in line with the three pillars of sustainable development (ecology, economy and society) to make sure, in particular, that local inhabitants would not have to suffer the kind of visual and olfactive pollution that can be associated with this type of development.


The Aïre STEP not only treats wastewater, it also treats the mud produced by all the water treatment plants in the canton. This centralised treatment generates nearly 7 million m3 of biogas, which is then used to meet the thermal energy needs of the plant.

A Few Figures

More than 80% of the Geneva region’s wastewater is treated by the STEP. More than 2,500 litres of wastewater enter the plant every second. More than 2,750 water samples are taken and 27,700 parameters are analysed in the laboratory every year.


Watch the video about water treatment, with commentary in French.