The Athens Water Supply and Sewerage Company (Greek: Εταιρεία Ύδρευσης και Αποχέτευσης Πρωτεύουσας, Eteria Ydrefsis ke Apohetefsis Protevusas, abbr.

Based in Galatsi in Athens, it is serving 4.3 million customers in the metropolitan area of Athens with fresh water and 3.5 million customers with sewers.

The Greek state holds a majority stake in EYDAP, with further 27 percent being listed at the Athens Exchange where it belongs to the 25 companies forming the FTSE/Athex Large Cap index.

Following the Greek government-debt crisis, EYDAP was planned to be fully privatized under the terms of the Eurozone Memorandum.

[5] Following this decision, a merger of EYDAP with the Thessaloniki Water Supply & Sewage Co. (EYATH) was taken into consideration instead.