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Drinking in the Ocean

Why Can't Humans Drink Salt Water?

More than 70% of the Earth is covered in water, but almost all of it is salt water that is found in the oceans around the world. Only about 2% of all water on Earth is pure enough to drink, but why is it that we can't drink salt water?

On the most basic level, people can't drink seawater because it is simply too salty. The processes used by our bodies to absorb water into each cell mean that we can't drink water that has too much salt in it. If you drink salt water, your kidneys begin to pump water out of your body, causing you to get dehydrated. It doesn't matter how much salt water you drink; your kidneys will begin to pump more water out of your body than you can make up for by drinking salt water.

Water is incredibly important for overall body function. Water makes up around 60% of the human body and is found in everything from blood to bones. Getting dehydrated can change the concentration of blood, for example, and make it harder for your heart to pump blood throughout your body. Your kidneys are responsible for regulating how much water your drink, how much you urinate, and the overall concentration of salt in your body.

If you eat very salty foods, or drink salt water, your kidney's first response is to send signals to your brain that tell you that you are thirsty. Hopefully, this causes you to start drinking pure water, which brings sodium concentration outside your cells down. The next step is to start pumping sodium out of your body, which is done through urination. Unfortunately, urine also contains water, and with the salt concentration in sea water being so high, it is impossible for our kidneys to pump out sodium fast enough. This causes us to get even more dehydrated and starts the whole process again.

What is Osmosis?

The cells in the human body absorb water through osmosis, a process where water molecules move from areas of high concentration to an area of low concentration across a semi-permeable membrane. The membranes of our cells only allow water to pass through and stop any other particles, including salt, from crossing into or out of the cell. Usually, the concentration of salt is about the same on either side of the cell.

The cells in the human body absorb water through osmosis, a process where water molecules move from areas of high concentration to an area of low concentration across a semi-permeable membrane. The membranes of our cells only allow water to pass through and stop any other particles, including salt, from crossing into or out of the cell. Usually, the concentration of salt is about the same on either side of the cell.

If you were to drink salt water, the amount of salt outside the cell would be much higher than the salt content inside the cell. To make up for this, cells release water molecules to try to make the concentration of salt on either side of the cell the same. This process of water moving out of the cell is dangerous, since our bodies need a certain amount of water in each cell to function properly. Eventually, this causes cells to shrivel up and even die altogether, leading to even more issues. The bottom line is that drinking salt water is never a good idea, even if it is the only source of water you have.

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Osmosis | Membranes and transport | Biology | Khan Academy

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Salt poisoningOsmosis in Simple EnglishOsmotic concentrationOsmosis

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