Question

Why can't you drink seawater even if you are stranded on a desert island?

Short answer

Seawater dehydrates the body due to its high salt content, exacerbating thirst and causing dangerous health effects such as hypernatremia.

Step-by-step solution

Understand Seawater Composition

Seawater contains a high concentration of salt, primarily sodium chloride. The salt content in seawater is approximately 3.5%, or 35 grams of salt per liter.

Osmosis and Cells

Consuming seawater causes the salt concentration in the body to increase. Through the process of osmosis, water moves from areas of low salt concentration (inside cells) to areas of high salt concentration (seawater) to balance the salt levels.

Dehydration Effect

As water is drawn out of the body's cells to counteract the high salt concentration, cells become dehydrated. This dehydration can lead to severe health effects, including organ failure.

Increased Thirst

Drinking seawater actually makes a person more thirsty because the body needs to expel the excess salt. This requires even more water than was originally consumed.

Health Risks

The excessive salt intake from seawater can lead to hypernatremia, a condition where there is too much sodium in the blood, causing symptoms like confusion, muscle twitching, and seizures.

Key concepts

Seawater Composition

Seawater is mostly water, but it has a lot of salt in it. The most common salt in seawater is sodium chloride, also known as table salt. For every liter of seawater, there are about 35 grams of salt. This high salt content is what makes seawater different from freshwater, like the water we drink from taps. Because of this difference, seawater is not suitable for drinking.

Osmosis

Osmosis is a process where water moves across cell membranes. It moves from areas with low salt concentration to areas with high salt concentration. If you drink seawater, the salt levels in your body go up. Water inside your cells will move out to balance the high salt concentration in your blood. This causes your cells to lose water and shrink. Osmosis keeps our body functioning properly by balancing fluid levels, but it can be harmful if too much salt is involved.

Dehydration

Dehydration happens when your body loses more water than it takes in. Drinking seawater speeds up dehydration. When your cells lose water due to osmosis, they can't function well. You might feel dizzy, tired, or even get headaches. Severe dehydration can damage organs and be life-threatening.

Hypernatremia

Hypernatremia is a medical condition characterized by high levels of sodium in the blood. Drinking seawater can lead to this condition. When there is too much sodium, your body tries to balance it out, which leads to water moving out from your cells. Symptoms of hypernatremia include confusion, muscle twitching, and seizures. It requires medical attention and can be deadly if not treated.

Health Risks

Drinking seawater poses serious health risks due to its high salt content. Excessive salt intake causes dehydration and hypernatremia. Your body will try to expel the extra salt, making you even more thirsty. This creates a vicious cycle: the more seawater you drink, the worse you feel. Long-term effects can include kidney damage and other organ failures. It's important to avoid drinking seawater even if you are very thirsty and stranded.