While water accounts for 71% of the Earth's surface, only 3.5% is safe for human consumption. Why is this so?

Saltwater of the Earth

Though water is crucial for human survival, and over 96% of the planet's liquid water is ocean water, the salt content of such water is too high for humans to consume.

According to the National Oceanic and Atmospheric Administration (NOAA), roughly 3.5% of seawater's weight comes from dissolved salt. If all of the oceans' salt were taken and spread over the Earth's entire land surface, the towering layer of salt would reach up to 166 meters in height, which is equivalent to the height of a 40-story building.

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Why Humans Can't Drink Seawater

According to RobDesalle, a curator at the American Museum of Natural History's Sackler Institute for Comparative Genomics, seawater saltiness, or salinity, is too high for humans to process safely.

DeSalle adds that the majority of animals have kidneys that can filter out water impurities. When one drinks saltwater, one ingests a tremendous amount of salt that the body must wash out.

The body typically does so in urine, produced by the kidneys by dissolving impurities within excess water. However, the kidneys can only make less salty urine than blood. The salt content of saltwater is roughly three times the amount present in human blood. This only implies that for every cup of saltwater drank, one may need to consume the same water volume for the kidneys to flush all the salt out.

DeSalle adds that drinking saltwater will never be able to quench thirst and will only increase it.

Though salt is crucial for maintaining chemical balances and reactions in the body, too much sodium intake could also be deadly. One may even end up dying of dehydration while getting thirstier.

Though humans cannot drink salt water, certain animals within ocean ecosystems have adaptations that enable them to ingest it safely.

For instance, seabirds, such as penguins and gulls, may spend weeks by the ocean with no freshwater. These creatures have unique bill grooves and salt glands that enable them to filter and purge surplus salt from ingested water before it reaches their stomach and gets absorbed within their blood.

Marine mammals, including dolphins and whales, have evolved adaptations to thrive in an environment where freshwater is either absent or scarce. DeSalle explains that marine mammals have adapted cellular structures and unique enzymes that enable them to purge the surplus salt out of their systems. He likens this to super kidneys.

As for humans, most human ancestors did not have any saltwater exposure. Natural selection ended up homing in on unsalted water processing. Human physiology also became remarkably fine-tuned to the point where saltwater disruptions could pose grave damages and dangers.

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RELATED ARTICLE: Drinking Tap Water: Is It Safe? How Can You Test Its Safety, Cleanliness?

Check out more news and information on Medicine & Health in Science Times.