Water-purifier - powered by the motion of the sea

I don't understand the science of it, but basically this "duck" is around 10 metres in diameter and 20 metres long. It rocks in the ocean and that movement causes the processes inside to desalinate sea water and send it to the shore along a pipe.

"One unit could produce 2000 cubic metres a day - enough to supply water to over 20,000 people."

A perfect item for survivalists to keep handy!