In the ancient times there was no organised sewerage system in the city of Athens. However, there are some reports of combined sewerage networks, wastewater and storm water run-off, but in these open sewerage systems stagnant waters were often sources of serious diseases, like cholera, plague, etc.

This practice continued for almost 15 centuries and was gradually phased out with the predominance of absorbing septic tanks. When septic tanks reached their saturation point, either a second tank was added or the waste was collected again and discharged into open streams or the sea.

1840-1930 Period
Circa 1840, for the first time in the modern history of Athens, the first combined flow sewerage system for collection and conveyance of wastewater and storm water runoff was constructed. A little later (1860), the existing Stadiou Street torrent from Syntagma Square to Omonoia Square was covered.

Between 1880-1890 the Kyklovoros open stream was covered with a large diameter stone duct (about 3 m). Until 1893 the total constructed combined network length was about 11,5 km while the urban development at that time required 90 km of sewerage network. The actual needs, in other words, were eight times more.

During the years 1893-1920, the Greek State successively invited different groups of experts from France, Germany and the USA to help finalize a strategy for solving the sewerage problem of Athens.

In the meanwhile, due to the influx of refugees caused by the 1922 Minor Asia disaster, the need for the construction of wastewater projects became imperative. As the water supply distribution networks expanded, the total quantity of potable water consumption increased, resulting in the subsequent increase of sewage produced and conveyed to the existing wastewater network.

In 1925, the municipality of Athens designed and constructed the “New Big Pipeline” while a large enlargement project was completed, the connection of the two “Big Pipelines” on the streets of Marni and Paionios .

In 1930 the construction of Prophet Daniel wastewater pipe ending in the area of the Faliriko Delta was completed. It was an oval pipe with a length of approximately 6,5 km overland and submarine about 700 m.

In 1931 the "Anonymous Sewer Construction Company of Athens and Environs" was established and the Greek State commissioned it the definitive study of the wastewater and rainwater network of Athens and Environs based on the preliminary design of the Italian Professor Fantoli, specific in hydraulics.

At the same time, the Municipality of Athens forbade the construction of absorbent cesspools on these roads where there was sewerage network and removed from individuals the right of construction and exploitation of sewage and storm water drains in the city. In the years 1934-1939 a large construction program was developed that included a drainage works covering 17 major streams, the construction of large pipelines on the streets of Rigillis and Vasilissis Sofias and the construction of flood protection ditch in Filopappou Hill.

At the same time three major infrastructure projects based on the study of Prof. Fantoli were built in Athens, despite the outbreak of the Second World War. These were involving:
  • The construction of the Central Sewerage Pipeline (CSP)
  • The construction of large and main collector after definitive study made for the Ilissos river.
  • The arrangement of the Kephissos river parts.
In the 1950s, Athens population began to expand exponentially. It was evident that the existing wastewater networks were insufficient.

The severe need for the planning and construction of large wastewater projects resulted in the establishment of the Athens Sewerage Organization. The Athens Sewerage Organization was the first company which undertook the design, construction, maintenance, operation and exploitation of the City’s wastewater and storm water drainage networks and managed successfully to set up strong and long-term foundations for the infrastructure of the Athens sewerage system.

Thus, in 1950, the preliminary design of the Athens Sewerage System began covering an area of 200,000 hectares. This study was finalized in 1963. The preliminary design was used as a basis for development of the city’s networks during the 1960s’ and 1970s’.

During the period of operation of the Athens Sewerage Organization between the years 1950 to 1980, sewage works of 1,700 km length and storm water works of 300 km length were constructed, including the Saronic Gulf Coastal Collector and the Collector Parakifissios.

1980- the Present
In 1980, the responsibilities of Athens Sewerage Organization were transferred to a new company established for the handling of water supply and sewerage needs of the greater Athens area, called EYDAP. In the sewage sector, this new organization undertook the collection and discharge of urban wastewater and industrial waste, as well as the expansion of the existing sewerage network whose total length is 6.000 km.

In the 1980s, the Supplementary Main Interceptor Sewer, another large diameter main collector, was added to the existing sewerage network of Athens.