El Magtaa desalination plant was until recently the world's largest reverse osmosis desalination plant producing 500K cubic meters of drinking water / day. It is built and operated by Singapore's Hyflux.
The Plant is located in western Algeria near Arzew (Mers El Hadjadj)
More info:
http://www.desalination.biz/news/news_story.asp?id=7802
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