if humans need salt, why does seawater dehydrate us?

Question

I’ve come to understand that the reason humans shouldn’t drink seawater is that it requires more water to get rid of that salt through urine. But if salt is a necessary nutrient, why would the body need to get rid of it at all? If your body were low on salt, what it be good for you to drink seawater?

Edit: added follow-up hypothetical question

In: Biology

Answer 1

Saltwater has too much salt, more than your body needs and more than your kidneys can filter out. So if you drink nothing but seawater, the salt levels in your blood rise too high, which kills you.