If you're using water at the end of a process that's just going to get mixed anyway, you're just extracting waste energy from the mixing process. Basically the

If you're using water at the end of a process that's just going to get mixed anyway, you're just extracting waste energy from the mixing process. Basically the fresh, used water and the highly saline water are in a lower-entropy state, and normally we'd just dump both in the ocean and allow the entropy to increase without extracting energy. But in this case we allow their entropy to increase in a controlled environment and so we're able to extract some energy in that process.