irradiated reproductive cells go brrr

No, you're missing the point again, when fish first went land diving they drank salt water because of that there body would have already had more salt and so would there kidneys, we evolved the ability to drink fresh water, that is what took a million years.

Well we were already adapted for it or at least our ancient ancient fish ancestors were we lost the ability that's my core point, salt isn't exactly rare and other minerals can be used to reduce osmotic pressure, but besides that 40% of all people live near salt water and ~30% of all land animals live near salt water so I wouldn't think that would be enough to lose such a valuable resource as water, I am obviously wrong since we can't drink salt water but it still feels like a miss step.