Some important concepts

1. Salt sucks up water. Water draws out salts. This is known as osmosis.

2. Your body Is a bag of salty soup. We call these body salts "electrolytes". You need electrolytes to live, and the electrolytes need water to be useful..

3. Your body pees regularly to get rid of stuff it doesn't need. Your body will always need to pee, regardless of how many electrolytes that water holds

4. Sea water is MUCH saltier than Saline

In short, you need to keep a balancing act. You need a certain amount of electrolytes to function, and you need a certain amount of water to hold those electrolytes. Your body uses water for different things tho, so you need to keep that balanced.

When you drink sea water, the water is MUCH saltier than your body. Instead of your body absorbing the water, the salt sucks water out of you, and you pee it out. Your body has less water at the end of the day.

If you drink pure, unsalted water though, the opposite happens. You drink the water, your body is saltier than the water. The water sucks out salt from your body, and you pee it out. You loose electrolytes.

Now, you don't wanna lose water. Dehydration causes a tone of issues. You also don't wanna lose electrolytes. That can cause just as many issues

Saline is a happy balance. it's only a little less saltier than your body, which means your body can take in water, pee it out, and lose little to no electrolytes. This lets someone who's dehydrated gradually rehydrate, without a drastic change in anything else.

This gradual change is often really important, because your body isn't a machine. It slowly adapts to extreme changes like starvation and dehydration to help you stay alive in those states. Quickly changing their intake (like giving a severely dehydrated person a gallon of fresh water) can really mess their body up if they aren't gradually introduced to it.