Harnessing the energy in waves always seemed like a terrible idea, since the waves are already relatively high entropy (like wind). But using waves to drive a mechanical desalination system makes a lot of sense. Loses due to energy conversion would be lower, since you're not converting it to another form of energy.

And of course this popular science article conveniently fails to mention the obvious downsides. A rogue wave would obliterate these machines. And who knows how much it will cost to clean the filter inlets of things like barnacles and algae.