According to scientific site, Earth Sky, the concentration of salt in the body is about 75 percent less than you would find in sea water. This means that drinking seawater would significantly increase the amount of salt in your bloodstream and the amount of work your body has to do to get rid of it.
Salt dehydrates, so the more saltwater you drink, the more water your body loses. As you drink seawater, the water already present in your body is rerouted to help your body dilute the excess of salt, according to the Marine Knowledge website. As result, other bodily functions start to suffer because of the lack of water in your system. Dehydration causes an increase in thirst, but it also causes you to urinate more often, as your body is trying to get rid of the excess of salt. More urine and less water worsens the dehydration problem.
Early Side Effects
Drinking saltwater will cause a number of early side effects as you get dehydrated. Dry mouth and rapid heartbeat are followed by low blood pressure, headaches and dizziness. Lethargy and confusion will eventually start to set in. Depending on how much sea water you had to drink and whether you're now drinking fresh water to eliminate the effects, you can also experience blood in the stool or vomit, loss of appetite and unconsciousness,
Serious Side Effects
If you continue drinking salt water even after noticing the initial side effects, your symptoms will get worse. According to the MedLine Plus, kidney failure will eventually occur if your body cannot longer produce urine because of lack of usable water. Severe dehydration can also lead to delirium, seizures and will ultimately kill you if not addressed. Even if you survive, permanent brain damage is possible.