FUKUOKA, April 3 -- A Japanese water plant is harnessing the natural process of osmosis to generate renewable energy that could one day become a common power source.

The possibility of generating power from osmosis - when water molecules pass from a less salty solution to a more salty one - has long been known.

But actually generating energy from that has proved more complicated, in part due the difficulty of designing the membrane through which the molecules pass.

Engineers in the city of Fukuoka and their private partners think they might have cracked it, and have opened what is only the world's second osmotic power plant.

It generates power from the transfer of molecules between treated sewage water and concentrated seawater, a was...