Seawater has a high salt concentration—about 3.5%, or 35 grams of salt per liter. The human kidneys are limited in how much salt they can filter out; they need

Seawater has a high salt concentration—about 3.5%, or 35 grams of salt per liter. The human kidneys are limited in how much salt they can filter out; they need a lower salt concentration than what seawater has to effectively expel salt. When someone drinks seawater, the kidneys are forced to use more water from the body to dilute and excrete the excess salt. This actually leads to a net loss of water, worsening dehydration instead of hydrating the body.