Energy will must be inputted into the system to do the filtering. Enthalpy is like a hooker, they give nothing away for free. Entropy is like a divorce and all is in chaos and greater disorder.
The amount of energy is the question. Reverse Osmosis systems require quite a pressure differential and that is generally provided by pumps pressurizing water. The graphene filters supposedly require very little pressure. Possibly so little that just letting ocean pipes 20 feet below sea level fill ground aquifers through a graphene filter would require nothing but gravity, and pumping water back up from the ground is the norm for utilities in places like CA.