The transfer of raw water sources (Reservoirs, Boreholes) to Water Treatment Plants (WTP) is done via an extensive external aqueduct system with a total length of 485 km.

The aqueducts are divided into:

  • Main (Mornos, Yliki) with a total length of 310 km.
  • Connecting  (Mornos-Yliki, Marathonas-Galatsi, Distomo) with a total length of 105 km.
  • Auxiliary, with a total length of 80 km.

The Aqueducts of Mornos and Yliki communicate with each other via connecting aqueducts. The existence of connecting aqueducts allows control, maintenance and repair of two aqueducts, with the possibility of closure of one of the two. In addition, it provides the possibility of alternative modes of exploitation of water resources, depending on the hydrological conditions and consumption needs.

Finally, despite the great distance of the main reservoirs (Mornos, Yliki) from Attica, the greater amount of water is transported via the aqueducts with the force of gravity without the economic and environmental impact of energy-intensive pumpings  with the exception of  emergency situations, e.g. pumping from Yliki from late 2007 to mid 2009.

Mornos Aqueduct
The maximum supply of the aqueduct from Mornos to Thebes is 23 cubic meters of water per second. Along the aqueduct there are remote control - remote control systems and dynamic regulation system, which guarantee the safe operation of the aqueduct. The Mornos aqueduct, outside Attica, supplies water to 18 municipalities and communities in the prefectures of Fokidos, Viotia and Attica, which are located along it
Yliki Aqueduct
The Yliki Aqueduct carries water from Yliki in the reservoir of Marathon and intermediately provides water to the Water Treatment Plant of Polydendri. It has a total length of 67 km and works with pumping. It consists of:
  • Canals with a total length of 23,7 km.
  • Siphons with a total length of 11,3 km.
  • Tunnels with a total length of 12,3 km.
  • Closed pipelines with a total length of 19,4 km
Mornos - Yliki Connecting Aqueduct
It interconnects the Mornos Aqueduct and Yliki Reservoir. It has a total length of 17, 9 km.

Marathonas - Galatsi Connecting Aqueduct
It carries water from Marathon reservoir in Galatsi Water Treatment Plant and has a total length of 21,5 km.

Distomo Connecting Aqueduct
The Distomo Aqueduct carries water from the Vasilica - Parori boreholes and from the Mavronero stream in the Mornos Aqueduct. It has a total length of 19 km.