Today’s Wonder of the Day was inspired by Luis. Luis Wonders, “why can we not drink salt water?” Thanks for WONDERing with us, Luis!

What do you like to do when you go to the beach? If you're like many kids, building a sand castle may be at the top of your to-do list.

If you're in the middle of a good book, you might prefer to sunbathe while you read a few chapters. Others may like to play sports, like beach volleyball. Whatever you choose to do, don't forget your sunscreen!

After a while out in the hot sunshine, you'll probably get thirsty. Fortunately, you're at the beach. All you need to do is head to the ocean to fill a glass with cool, thirst-quenching water from the sea, right?

Of course not! The thought of drinking a big gulp of water from the ocean probably makes you pucker up. If you've ever swam in the ocean, you know that the water is salty and doesn't taste good at all.

The salty taste of water from the ocean isn't the main reason we human beings don't drink saltwater, however. There's an important scientific reason why we need to drink freshwater rather than saltwater to stay healthy.

Over 70% of Earth's surface is covered with water. Most of that water, though, is undrinkable saltwater. The fact that we can't drink saltwater might seem odd when you consider that our bodies need both water and salt to function.

The problem with saltwater is the amount of salt in it. Our bodies only need a small amount of salt. When we take in too much salt, our kidneys must get rid of the excess salt through our urine.

Human blood has a salinity of 9, which means there are 9 grams of salt and 991 grams of water in every 1,000 grams of fluid. Saltwater is considered a hypertonic fluid, which means it contains more salt than human blood. In fact, saltwater has a salinity of 35 — that's approximately four times the salinity of blood.

Drinking saltwater would result in your body getting rid of the excess salt by urinating more water than you took in. Instead of quenching your thirst, your body would actually suffer a net loss of water, resulting in dehydration and increased thirst.

In addition to depleting your body's water supply, drinking saltwater can also lead to muscle cramps, nausea, and high blood pressure. If you were to continue to drink saltwater instead of freshwater, you would eventually experience even worse effects, such as organ failure, coma, and even death.

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