Fresh water—or treated wastewater—is placed on one side of a membrane. On the other side is seawater, made even saltier by concentrating leftover brine from a desalination process. The difference in saltiness pulls the fresh water across the membrane, increasing the pressure on the saltwater side. That pressure is then used to drive a turbine, generating electricity.

So you take wastewater that I guess is clean but not clean enough for human consumption and take your leftover brine from your desalination plant, mix 'em, get some juice, release the brine back into the ocean, and use the power to generate fresh water from sea water and create new brine.

I guess that system is what made the most sense but it kinda sounds like someone describing their concept for a perpetual motion machine.