The power and water purchase agreement is due to be concluded on 28 August, according to the Belgian firm.
The Suez-led consortium emerged as the low bidder for the project in July after it submitted a price of BD13.972 ($37.1) a megawatt hour (MWh) of power.
A second group of Saudi Arabia's Acwa Power Projects and Korea Electric Power Corporation offered a tariff of BD14.725 a MWh.
The water tariff was fixed for all bidders at BD0.350 a cubic metre, equivalent to BD1.59 a thousand gallons.
The IWPP will have a capacity of 1,100-1,250MW of power and 48 million gallons a day of desalinated water (MEED 24:07:08).