The sewerage of the Athens Metropolitan Area consists of both storm water runoff and sewage pipes. The storm water runoff flows reach, via gravity flow, the sea (Saronic Gulf) and the sewage pipes discharge at the Psyttalia island sea region after undergoing wastewater treatment at the Psyttalia Wastewater Treatment Plant.

The total length of the network is 6,000  km and covers 92% of the wastewater needs of Attica.  Only 250 km of the total drainage system  reach central wastewater system and cover the needs of the centre of Athens. A separate system with separate storm water and wastewater networks  applied on the rest length of the sewerage network.

The large diameter sewers run through areas where the slopes permit the conveyance of the wastewater by gravity (gravity sewers) with only exception the Saronic Gulf Coastal Collector, which operates with the assistance of 44 pumping stations.