Water is essential to our survival, and yet more than 96% of the liquid water on the planet is ocean water - and contains so much salt that humans can't drink it.
Salty seawater does not quench thirst, and excessive drinking can even lead to death due to dehydration, writes the Live Science newsletter.
Why salt water can not quench thirst
The answer to this question is quite simple: salt water is simply too salty for our kidneys to handle.
According to the National Oceanic and Atmospheric Administration (NOAA), about 3.5% of the weight of seawater consists of dissolved salt. If all the salt in the oceans were removed and distributed over every land surface on Earth, the salty layer would rise to a height of more than 166 meters - roughly a 40-story office building.
"The salinity of seawater is too high for humans to process safely, because our cells need water in a relatively pure form," said Rob Desall, curator of the Sackler Institute for Comparative Genomics at the American Museum of Natural History in New York.
When we drink salt water, we consume a lot of salt, which the body must flush out of the body. The kidneys filter out impurities from the water, but they can only produce urine, which is less salty than our blood. This means that for every cup of salty water you drink, you need to drink at least that much water so that your kidneys can flush out all that salt.
"You might say, "Why not just drink more salt water?" But then you just end up with more salt, which you then have to rinse out with more water. So, salt water can never quench your thirst - it can only make you thirsty," the scientist explained.
Some animals, such as seabirds and marine mammals, have adaptations that allow them to drink salt water. However, most land animals, including humans, have evolved to drink only fresh water. This is because our primate ancestors lived in an environment where fresh water was more readily available than salt water.
Salt water cannot quench human thirst because it is too salty for our kidneys. Some animals, such as seabirds and marine mammals, have adaptations that allow them to drink salt water, but most land animals, including humans, have evolved to drink fresh water.
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