In the early 1900’s, Athens’ rapidly increasing population called for the city to grow and expand at a similar rate. This rapid development demanded that immediate action be taken regarding water supply. In 1922 with the huge influx of refugees from Asia Minor, Athens underwent a sharp increase in population that had a devastating effect on the city’s water supply. An American Company by the name ULEN Company was commissioned to renovate and increase the water supply capacity of the Hadrian Aqueduct system, as well as to construct a new water supply system for the Athens and Piraeus area.
Thus in 1925 a contract was signed between the Greek Government, the Bank of Athens and the American Firm ULEN for the financing and construction of the new water supply works. The result of the contract was the formation of a company with the name "The Greek Water Company S.A." (with the acronym EEY), whose sole purpose was to construct and operate water supply works for Athens.
The first major project was the construction of Marathon Dam (1926-1929), with a total height of 54 m. and a length of 285 m. Over 900 people were involved in the construction of the dam, which is considered unique because it is entirely paneled externally with Pentelikon white marble.
The Boyati Tunnel was constructed to transport water from the Marathon impounding reservoir to a new water treatment plant in Athens. The Marathon dam, the Boyati Tunnel, the Galatsi Water Treatment Plant and the new water distribution networks for the city of Athens and Piraeus represent the first modern attempt to provide a total solution to the city’s water supply needs.
In the years that followed (1950’s) Athens’s population continued to grow and the need for additional sources of water once again became pressing. Yliki Lake in the nearby prefecture of Viotia had a significant amount of available water, however, it required the construction of pumping facilities in order to transport the raw water to Athens. The Yliki pumping station and the aqueduct system began operation in 1959 and today has a nominal supply of 750.000 cubic meters/day.
In 1974 the ULEN Company withdrew from the ownership of the Greek Water Supply (EEY), leaving the operation of the Athens water supply to the remaining Greek partners. In 1980, a new law was passed that called for the merger of the Greek Water Supply Company (EEY) and the Athens Sewerage Organization (with the acronym OAP). This merger resulted in the formation of a new water authority (with the acronym EYDAP) responsible for the operation of the city’s water supply, sewerage and storm drainage networks.
With Athens continuing need to increase raw water supplies, a new project was proposed which involved the damming of the Mornos River (approximately 200 km. from Athens). The dam’s construction began in 1969, but operation of the Mornos dam and new Mornos aqueduct officially began in 1981. The Mornos dam is one of the highest earth gravity dams in Europe with a height of 126 m. The Mornos impoundment reservoir has a storage capacity of 780 million cubic meters of water. The Mornos aqueduct that transports water from the Mornos reservoir to Athens is the second longest aqueduct in Europe with a total length of 192 km.
Another major project, which has provided Athens with additional water, is the Evinos River diversion to the Mornos Impounding Reservoir. The project consists of the Evinos Dam and a diversion tunnel. Work began on the Evinos project in 1992. The diversion tunnel was completed in just two years, which is considered to be a significant achievement given the project scale. The tunnel has a length of 29.4 km and transports approximately 100 million cubic meters of water per year.
The Mornos and Yliki Aqueducts are joined by a system of interconnecting aqueducts that provide alternative supply schemes for the maintenance and repair needs of the works. The network of interconnecting aqueducts also offers EYDAP greater overall control and water resource management capability.
Via the Mornos, Yliki and other interconnecting aqueducts (total combined length of 500 km.), raw water is transported from various sources to the four drinking water treatment plants in the Athens area: Galatsi, Polydendri, Acharnon, and Aspropirgos. The four water treatment facilities have a combined capacity of 1.9 million cubic meters of water per day. The treatment of raw water involves the processes of coagulation, sedimentation, sand filtration and finally disinfection with chlorination.
Athens’ drinking water is of excellent quality and is considered to be one of the best in Europe. Drinking water is transported from the four treatment plants to the 50 storage reservoirs and tanks throughout the city. From the storage reservoirs, water reaches the consumers through an extensive distribution network with an estimated total length of 7,55 million meters, which is constantly expanding and being refurbished.