RIYADH, Aug 2 (Reuters) - Saudi Arabia's Water and Electricity Co. (WEC) has invited expressions of interest in a project to develop a reverse osmosis desalination plant in Rabigh, according to a tender posted on its website on Wednesday.

The project, to be located about 150 km north of Jeddah, the kingdom's second-biggest city, will produce 600,000 to 1.2 million cubic metres of potable water per day, the statement said. Power supply will be provided from the high voltage network. The deadline for parties to show their interest is August 21.

The mainly state-owned WEC is offering a 25-year concession to the winning developer or consortium to sell the plant's output under a water purchase agreement (WPA) with the Saudi government.

WEC was established in 2003 to sell water and electricity to the kingdom's state-owned Saline Water Conversion Corporation (SWCC) and state-controlled Saudi Electricity Company (SEC).

Banque Saudi Fransi is financial adviser, DLA Piper Middle East is legal adviser and Fichtner GmbH & Co. KG is technical adviser for the project.

(Reporting by Katie Paul; Editing by Saeed Azhar) ((Katie.Paul@thomsonreuters.com;))