seawater is saline, you have to be careful what you do with it because you dont want to literally salt the earth where you are (soil remediation friggin sucks).

seawater is also not valuable. You don't care about the water quality in the reservoir, you just let it fall back into the sea. If it evaporates you're losing energy but you aren't losing potable water that you sell, and it doesn't require a connection to a water distribution main.

I imagine the main difference would be salt content, but I can't speak to how that would affect things.