The thermodynamic cost of separating salt from water is the same per molecule no matter what. It's a fundamental physical limit. RO can be more efficient than

The thermodynamic cost of separating salt from water is the same per molecule no matter what. It's a fundamental physical limit. RO can be more efficient than electrolysis. The major factor is that electrolysis wastes a good fraction of the input energy on heating the water. On the other hand, RO requires high pressures, which is energy intensive. RO is generally more efficient overall, but either way you have to pay the cost of reversing entropy.