... like I'm 5 years old
We've all had that moment at the beach where a wave unexpectedly crashes into us and we get a mouthful of salty ocean water. It tastes terrible, but beyond that, why is it harmful to drink ocean water?
Simply put, drinking seawater can dehydrate you. This might sound counterintuitive because when we think of drinking anything, we usually think of quenching our thirst. But the salt in seawater is the problem. Our bodies need a certain concentration of salt to function. If we take in too much salt, our bodies need to get rid of the excess. We do this by urinating more, which can lead to dehydration.
Imagine being really thirsty and deciding to drink from a bottle labeled 'water.' You expect to be refreshed, but instead, you find it's filled with salt. Not only does it taste awful, but you're even thirstier than before. That's what drinking seawater is like.
... like I'm in College
On a more detailed level, the reason why drinking seawater can lead to dehydration has to do with the way our kidneys function. The kidneys are responsible for filtering waste products and extra fluid from our blood, which then gets excreted as urine. However, the kidneys need water to do this job.
When we consume seawater, the high salt content increases the concentration of our blood. Our kidneys then have to work harder to remove this excess salt. But to do this, they need more water. The result is that we urinate more, losing more water from our bodies, which leads to dehydration.
Think of your body as a Lego structure. The bricks represent the cells, and the tiny gaps between the bricks represent the salt in your body. When you drink fresh water, it's like adding more bricks to the structure, making it bigger and stronger.
But when you drink seawater, it's like pouring a bucket of tiny Lego pieces into your structure. These pieces get stuck in the gaps and start pushing the bricks apart. Your body then has to use its bricks (water) to try and remove these extra pieces. This leads to more and more bricks being removed from the structure, making it weaker. That's dehydration. Your body becomes weaker because it's using its resources to try and remove the excess salt instead of strengthening itself.
... like I'm an expert
From a biological and physiological perspective, the ingestion of seawater can lead to a condition known as hypernatremia. Hypernatremia is an electrolyte imbalance where there is a high level of sodium in the body.
When sodium levels become too high, water moves from cells into the bloodstream to try and dilute the sodium. This causes cells to shrink, which can lead to serious health problems, including neurological symptoms, kidney damage, and, in extreme cases, death.
Moreover, the kidneys have a limit to how much salt they can process. The average human kidney can only produce urine that's less salty than seawater. Thus, for every glass of seawater you drink, your body would need to pee out more than a glass of water to remove all the extra salt, which only serves to dehydrate you more.